JP2001348218A - SiGe CRYSTAL AND MANUFACTURING METHOD THEREOF - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a SiGe crystal formed which not only attains large effects to have high performance index as a thermionic element, excellent workability and to be free from characteristic degradation or the generation of crack in use but stably attains the high performance index by being controlled to a dopant concentration to attain the high performance index, the manufacturing method thereof and the thermionic element using the crystal. SOLUTION: The size of the grain of the crystal is controlled to >=5×10-5 mm3 and the electrical resistance is controlled to 1×10-5-1×10-4 Ωm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to silicon germanium (SiGe) which is suitably used as a thermoelectric element material.
The present invention relates to a crystal, a method for producing the crystal, and a thermoelectric element using the crystal.

[0002]

2. Related Art When a p-type semiconductor material and an n-type semiconductor material are joined at two locations and a temperature difference is applied between the two locations, heat is applied between the two locations due to the so-called Seebeck effect. An electromotive force is generated.

Since a thermoelectric element applying this principle has no moving parts and has a simple structure, there is a possibility that a thermoelectric element having a high reliability, a long service life, and easy maintenance can be used. Is high. For this purpose, various thermoelectric element materials have been conventionally manufactured and developed.

[0004] Among them, SiGe is known as a chemically stable and typical thermoelectric element material, and many proposals have been made with respect to its performance improvement and manufacturing method as compared to the prior art (Japanese Patent Application Laid-Open No. 61-149453). (US Patent No. 471
1971; European Patent No. 185499);
No. 56020, Japanese Patent No. 2623172, etc.].

[0005] A performance index Z, which is an index of the performance of a thermoelectric element, is given by the following equation (1). Z = α ² σ / k. . . . . . . . . (1) [in the formula (1), α: Seebeck coefficient, σ: electric conductivity,
k: thermal conductivity. ]

The performance index Z of various thermoelectric element materials is expressed as shown in FIG. 2 in relation to the temperature. As is clear from FIG. 2, in the case of the SiGe polycrystal obtained by the conventional manufacturing method, 200 ° C. or more, which is called a practical temperature range,
Particularly in the region up to 600 ° C., for example, the tellurium-based material B
The inferiority of the figure of merit Z as compared with i ₂ Te ₃ or PbTe was a practical weak point.

Therefore, in order to improve the figure of merit Z, the concentration of conduction electrons and holes in the material is increased to increase the electric conductivity.
Group V elements such as P, As, and Sb as n-type materials may be added as dopant.
As disclosed in Japanese Patent No. 4953 and Japanese Patent Application Laid-Open No. 8-56020, attempts have been made to add metals such as Pb, Sn, Fe, Ni, Cr and silicides thereof.

Although these improvements have improved the performance index Z of SiGe, further improvement in the performance index is required for practical use.

In addition, a conventional SiGe ingot is prepared by mixing a predetermined amount of Si, which is a constituent component, an additive such as Ge and a dopant, and then dissolving the mixture to obtain a composition as uniform as possible, followed by cooling, or cooling. In addition, since the mixture is produced by a powder sintering method, the obtained ingot is an aggregate of crystal grains.

[0010] For this reason, there have been the following obstacles to prevent full-scale practical use. Carrier scattering at crystal grain boundaries is unavoidable, which hinders improvement in electrical conductivity. Grain boundary segregation occurs in a portion close to a high temperature heat source of 200 ° C. or higher, particularly 500 ° C. or higher, which is a practical temperature range, and the characteristics deteriorate with time. Since local inhomogeneity of the composition is unavoidable, this leads to further deterioration of the properties, and cracks are liable to occur during processing and use.

In view of the above-mentioned problems of the polycrystalline SiGe produced by the conventional manufacturing method, the present inventors have conducted intensive studies and found that the size of the crystal grains constituting the SiGe crystal block was increased. Preferably, a single crystal is used, which solves the above-mentioned problems and can be used for practical use.
e The idea of realizing a thermoelectric element was considered, and as a result of actually examining various methods, a Czochralski method was used.
We succeeded in producing a SiGe crystal ingot having a crystal grain size of 5 × 10 ⁻⁵ mm ³ or more over almost the entire x of _x Ge _1-x (0 <x <1), and as a thermoelectric element We have already proposed a novel SiGe crystal material which has improved performance index and excellent workability and does not cause special deterioration or cracks during use (Japanese Patent Application No. 10-335894).

[0012]

According to the above-mentioned proposal (Japanese Patent Application No. 10-335894), SiGe is improved in the figure of merit as a thermoelectric element, has excellent workability, and does not cause characteristic deterioration or cracks during use. Although a crystalline material has been obtained, further improvement in the figure of merit is required. We continue to use this new SiGe
We have gained new insights by conducting research on crystals, and have extended our proposals.

Hereinafter, the formation of the present invention will be described. The performance index Z, which is an index of the performance of the thermoelectric element, is proportional to the product (α ² σ) of the square of the Seebeck coefficient (α) and the electrical conductivity (σ) as shown in Expression (1). Therefore, one way to improve the figure of merit Z is to increase this product (that is, to increase both α and σ at the same time).
According to various investigations, it has been found that α has a decreasing relationship with σ and α and σ cannot be increased simultaneously. Therefore, as a result of conducting an experiment shown in Experimental Example 1 described later to obtain an optimal value of α ² σ from the relationship between α and σ, it was found that α ² σ has a peak with respect to σ, Completed.

The present invention provides a dopant which not only has a high performance index as a thermoelectric element, is excellent in workability, and has a great effect of not causing characteristic deterioration or cracking during use, and also has a high performance index. An object of the present invention is to provide a SiGe crystal, a method for producing the same, and a thermoelectric element using the crystal, which can stably obtain a high figure of merit because the concentration is controlled.

[0015]

In order to solve the above problems SUMMARY OF THE INVENTION, Si _x Ge _1-x of the present invention (0 <X <1) crystal size of the crystal grains constituting the crystal 5 × 10 ^{- 5} mm ³ or more, and the electrical resistivity is in the range of 1 × 10 ⁻⁵ to 1 × 10 ⁻⁴ Ωm. The electric resistivity is 2 × 10 ⁻⁵
It is preferably in the range of 7 × 10 ⁻⁵ Ωm.

Further, according to the present invention, Si _x Ge _1-x (0 <X <
1) The crystal has a crystal grain size of 5 × 10
^-5 mm ³ or more, and the dopant concentration is in the range of 0.8 × 10 ^{19 to} 1.5 × 10 ²⁰ atoms / cm ³ in the case of p-type,
In the case of a mold, the range is 4 × 10 ¹⁸ to 8 × 10 ¹⁹ atoms / cm ³ . When the dopant concentration is p-type, the range is 1.3 × 10 ^{19 to} 6 × 10 ¹⁹ atoms / cm ³ ;
In the case of the n-type, it is preferably in the range of 0.7 × 10 ¹⁹ to 4 × 10 ¹⁹ atoms / cm ³ .

The method for producing a _{Si x Ge 1-x (0} <X <1) crystal of the present invention, Si _x Ge _1-x by the Czochralski method
When the crystal of (0 <X <1) is pulled, the dopant concentration of the pulled crystal is 0.8 × 10 ¹⁹ to 1.
5 × 10 ²⁰ atoms / cm ³ range, 4 × 10 ^{18 for} n-type
The crystal is pulled up by controlling the doping amount so as to be up to 8 × 10 ¹⁹ atoms / cm ³ .

At this time, the dopant concentration is in the range of 1.3 × 10 ^{19 to} 6 × 10 ¹⁹ atoms / cm ³ for p-type,
In the case of a mold, it is preferable to pull the crystal by controlling the doping amount so as to be in the range of 0.7 × 10 ¹⁹ to 4 × 10 ¹⁹ atoms / cm ³ .

Further, the thermoelectric element of the present invention has the above-mentioned S
and is characterized in the use of crystals of _{i x Ge 1-x (0} <X <1).

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below, but it goes without saying that various modifications can be made without departing from the technical idea of the present invention.

In order to obtain a crystal of Si _x Ge _1-x (0 <X <1) according to the present invention, a crystal pulling apparatus generally used by the Czochralski (CZ) method may be used.
Using this apparatus, the required Si, Ge and dopant (p
Boron, gallium, etc. for the type, phosphorus for the n-type,
Arsenic, antimony, etc.) in a quartz crucible, for example, using an Si single crystal as a seed crystal and argon gas (1 atm)
If the crystal is pulled at a pulling speed of 1 to 10 mm / Hr, the size of the crystal grains is 5 × 10 ⁻⁵ mm ³ or more (the average particle size is about 5
Si _x Ge _1-x (0 over 0 .mu.m) <can be raised crystals of X <1).

In the present invention, the electrical resistance of the pulled crystal is
1 × 10^-Five~ 1 × 10^-FourΩm range
To control the amount of dopant dissolved in the quartz crucible.
Need to be adjusted. Therefore, dopa in the pulled crystal
0.8 × 10 for the p-type¹⁹~ 1.5 × 1
0²⁰atoms / cm^Three, Preferably 1.3 × 10¹⁹~ 6
× 10¹⁹atoms / cm^ThreeAnd the n-type
4 × 10 in case^{1 8}~ 8 × 10¹⁹atoms / cm^ThreeRange, good
Preferably 0.7 × 10¹⁹~ 4 × 10¹⁹atoms / cm ^ThreeRange
The crystal is pulled up by controlling the doping amount so that Real
The amount of dopant added to the quartz crucible at the time
Type and segregation coefficient, and amount of Si and Ge
In the ordinary CZ method,
It can be easily determined.

The Si _x Ge thus pulled up
The crystal of _1-x (0 <X <1) has a crystal grain size of 5 × 10 ⁻⁵ mm ³ or more and an electric resistivity of 1 × 10 ⁻⁵ mm ³ or more.
× 10 ^{- 5} to 1 for the range of × 10 ^-4 [Omega] m, the performance index is stably high, damage or cracking is less likely. Therefore, if the thermoelectric element is formed by performing the usual processing, a thermoelectric element having excellent performance can be obtained.

[0024]

The present invention will be described in more detail with reference to the following experimental examples.
Will be described. (Experimental example 1) The dopant of the dopant was obtained by the Czochralski method.
5 types with different types, dopant concentrations and SiGe compositions
Crystals (A to E) are pulled up and each temperature is 1000K
Coefficient α, electrical conductivity σ (electrical resistivity
ρ), measure the thermal conductivity k and calculate α ^Twoσ was calculated. Table 1
FIG. 1 shows the electrical resistivity and α^Two
The relationship with σ was plotted.

The methods for measuring the physical properties are as follows. In addition, microscopic observation revealed that each crystal had a crystal grain size of 5 × 10 ⁻⁵ mm ³ or more (average particle size of about 50 μm or more).

Measurement of Seebeck coefficient A disk-shaped sample having a diameter of 10 mm and a thickness of 1 mm was cut out from the pulled crystal, and the Seebeck coefficient was measured by a temperature difference method using the sample. The temperature difference method is a method of measuring a thermoelectromotive force generated on both contact surfaces of a sample sandwiched between heat blocks having different temperatures.

Measurement of Electric Conductivity A sample of 3 × 1 × 10 mm ³ was prepared from the pulled crystal, and the electric conductivity was measured by a four probe method. The four-probe method
In this method, a current is applied from two outer needles of four needles arranged in a straight line, and a potential difference generated between two inner needles is measured.

Measurement of Thermal Conductivity A disk-shaped sample having a diameter of 10 mm and a thickness of 1 mm was cut out from the pulled crystal, and the thermal conductivity was measured by a laser flash method. The laser flash method is a method of irradiating the surface of a sample with a laser instantaneously and evaluating the thermal conductivity based on a temperature change on the back surface.

From FIG. 1, α ² σ indicates that the electric resistivity ρ is 1 × 1
0 ^-5 to 1 × 10 ^-4 Ωm (that is, electric conductivity σ).
Has a peak at 1 × 10 ⁵ to 1 × 10 ⁴ (1 / Ωm)). In particular, ρ is 2 × 10 ^{−5 to} 7 × 10 ⁻⁵ Ωm (σ is 5 ×
It was found that the maximum value was observed at around 10 ^{4 to} 1.4 × 10 ⁴ (1 / Ωm).

[0030]

[Table 1]

[0031]

As described above, according to the present invention, the Si _x Ge _{1-x of the} present invention is used.
According to the crystal of (0 <X <1), the thermoelectric element has a high figure of merit, is excellent in workability, and has not only a great effect of preventing property deterioration and cracking during use but also has a high effect. Since the dopant concentration is controlled to obtain a figure of merit, a high figure of merit can be stably obtained. Further, according to the present invention, the Si _x Ge _1-x
Crystals of (0 <X <1) can be efficiently produced.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between electrical resistivity and α ² σ in Experimental Example 1.

FIG. 2 is a graph showing the relationship between the performance index of various thermoelectric element materials and temperature.

Claims (7)

[Claims] 1. The size of a crystal grain constituting a crystal is 5 × 1.
0 ^-5 mm ³ or more, and the electric resistivity is 1 × 10 ^-5 to 1 ×
Characterized in that it is in the range of _{^{10 -4 Ωm Si x Ge 1-}} x
Crystals of (0 <X <1). 2. The electric resistivity is 2 × 10 ^{−5 to} 7 × 10.
^2. The S according to claim 1, wherein said S is in the range of ^-5 .OMEGA.m.
crystal of _{i x Ge 1-x (0} <X <1). 3. The size of a crystal grain constituting a crystal is 5 × 1.
0 ⁻⁵ mm ³ or more, and the dopant concentration is in the range of 0.8 × 10 ^{19 to} 1.5 × 10 ²⁰ atoms / cm ³ in the case of p-type,
For n-type crystals, characterized in that in the range of ^{4 × 10 18 ~8 × 10 19} atoms / cm 3 Si x Ge 1-x (0 <X <1). 4. The dopant concentration is in the range of 1.3 × 10 ^{19 to} 6 × 10 ¹⁹ atoms / cm ³ for p-type, and 0.7 × 10 ¹⁹ to 4 × 10 ¹⁹ atoms for n-type. / Si _x Ge _1-x, wherein the cm in the range of ³ (0 <X <1) crystal. 5. The method according to claim 1, wherein the Si _x Ge _{1-x is formed} by the Czochralski method.
When the crystal of (0 <X <1) is pulled, the dopant concentration of the pulled crystal is 0.8 × 10 ¹⁹ to 1.
5 × 10 ²⁰ atoms / cm ³ range, 4 × 10 ^{18 for} n-type
The Si _x Ge _1-x (0) is characterized in that the crystal is pulled up by controlling the doping amount so as to become ８8 × 10 ¹⁹ atoms / cm ^3.
<X <1) A method for producing a crystal. 6. The dopant concentration is in the range of 1.3 × 10 ^{19 to} 6 × 10 ¹⁹ atoms / cm ³ for p-type, and 0.7 × 10 ¹⁹ to 4 × 10 ¹⁹ atoms for n-type. / Si according to claim 5 cm ³ range so as to control the doping amount of wherein the pulling crystal _{x Ge 1-x (0 <} X
<1) A method for producing a crystal. 7. The Si according to claim 1, wherein
_A thermoelectric element using a crystal of _x Ge _1-x (0 <X <1).