JP2012253178A - Thermoelectric conversion element, method for manufacturing the same, and thermoelectric conversion module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoelectric conversion element having high thermoelectric conversion efficiency, and a method for manufacturing the same.SOLUTION: The thermoelectric conversion element comprises a semiconductor material, i.e., a thermoelectric conversion material, at least one nanowire electrically connected to the semiconductor material, and an electrode electrically connected to the nanowire. The nanowire comprises a semiconductor base material and a dopant deposited on a surface of the semiconductor base material.

Description

  The present invention relates to a thermoelectric conversion element that converts heat into electricity and a method for manufacturing the same. Moreover, this invention relates to the thermoelectric conversion module which has the said thermoelectric conversion element.

In recent years, power generators have been developed that use heavy metals such as Bi, Te, and Pb as thermoelectric conversion elements to reduce the heat generated in huge facilities to electric power. Thermoelectric conversion is the conversion of thermal energy into electrical energy. This thermoelectric conversion is based on the Seebeck effect in which, when two kinds of materials are joined together and a temperature difference is generated at both ends, a voltage is generated so as to go against the temperature gradient. For example, a bulk semiconductor material having a high carrier mobility at room temperature, such as Bi ₂ Te ₃ , is doped with two types of semiconductor substances, an n-type semiconductor in which electrons move and a p-type semiconductor in which holes move, A thermoelectric conversion element sandwiched between two metal electrodes in the low temperature part is produced. As a result, electron / hole carriers flow from the high temperature portion to the low temperature portion, and an electromotive force is generated to generate power. In a thermoelectric conversion device in practical use, the power generation efficiency is increased by arranging a plurality of these basic elements into a module.

  In addition, structures and materials that improve power generation efficiency have been proposed (see, for example, Non-Patent Documents 1 to 3). In Non-Patent Document 1, the efficiency of thermoelectric conversion using cobalt oxide is measured. Non-Patent Document 2 discloses spin thermoelectric conversion using a magnetic material by the spin Seebeck effect using spin current. Further, Non-Patent Document 3 shows that thermoelectric conversion efficiency is greatly increased by making a normal silicon material into a low-dimensional nanowire structure.

  In addition, means for improving the reliability of the thermoelectric conversion element is also disclosed (for example, see Patent Documents 1 and 2). In Patent Document 1, at least one of a substrate and an electrode in contact with the substrate has electrical insulation, and the substrate and the electrode are joined by a liquid metal. A thermoelectric conversion element is disclosed in which a semiconductor junction contains metal fibers. Patent Document 2 discloses a thermoelectric conversion element having a stress relaxation layer made of a carbon nanotube including a p and n thermoelectric semiconductor pair sandwiched between a pair of opposed electrodes and containing a metal between the electrode and the thermoelectric semiconductor. Has been.

JP 2010-98035 A JP 2010-205977 A

I. Terasaki et al., "Large thermoelectric power in NaCo2O4 single crystals", Physical Review B, 1997, 56, 20, R12585 K. Uchida et al., “Spin Seebeck insulator”, Nature Materials, 2010, 9, 894. A. I. Hochbaum et al., “Enhanced thermoelectric performance of rough silicon nanowires”, Nature, 2007, 451, 163.

  The following analysis is given from the perspective of the present invention.

  There are several problems with thermoelectric conversion elements using bulk high mobility semiconductors currently used at room temperature. The first problem is that these bulk semiconductor materials have low oxidation resistance and are susceptible to degradation due to their structure. For this reason, it is not easy to process the semiconductor material, and with this semiconductor material, it is not possible to further increase the efficiency of thermoelectric conversion. The second problem is that it is difficult to control at the atomic level in the contact junction with the metal electrode, so that metal atoms and semiconductor atoms are mixed by atomic diffusion in the contact junction between the metal electrode and the bulk semiconductor material. That's what it means. For this reason, thermoelectric efficiency will fall significantly.

  In the thermoelectric conversion element described in Patent Document 1, metal fibers are provided between the electrode and the thermoelectric semiconductor in order to improve adhesion and ensure high thermal conductivity. However, if the thermal conductivity is increased, the thermoelectric efficiency cannot be improved. Also in the thermoelectric conversion element described in Patent Document 2, the thermal conductivity is increased when a metal is included in the carbon nanotube. Therefore, when the stress relaxation layer described in Patent Document 2 is used, thermoelectric efficiency cannot be improved.

In general, in a thermoelectric conversion element, the conversion efficiency η from heat energy to electric energy can be expressed as the following Expression 1. Here, T _H is the temperature of the high temperature part, T _C is the temperature of the low temperature part, and T is the average temperature T = (T _H + T _C ) / 2. Z is called a thermoelectric figure of merit, and is a physical quantity specific to the material determined by the substance and its structure, and is expressed by the following formula 2. G is the electron / hole carrier conductivity. κ is the thermal conductivity. S is the Seebeck coefficient. The Seebeck coefficient S is a physical quantity specific to the material, and is determined by the mobility of carriers of electrons and holes that flow and the density of states on the Fermi surface.

[Formula 1]

[Formula 2]

  The conversion efficiency η shown in Equation 1 is a function that increases monotonously with respect to the variable ZT, and obtaining a large ZT leads to the construction of a highly efficient thermoelectric conversion element. The electromotive force ΔV obtained by the power generation by the temperature gradient is expressed as in Equation 3 using the Seebeck coefficient S and the temperature difference ΔT. Therefore, to achieve high thermoelectric efficiency, it is necessary to increase the conductivity of the carrier while reducing the thermal conductivity. Further, when high carrier conduction is obtained, the electromotive force obtained is increased accordingly.

[Formula 3]

  In general, if this dimensionless amount of ZT exceeds 1, it is said that the thermoelectric exchange performance is excellent. In a normal substance, the higher the electron mobility, the higher the thermal conductivity, and the performance evaluation index ZT does not increase and the thermoelectric conversion function decreases. A high mobility bulk semiconductor material containing a rare metal, which is currently in practical use, is a layered compound having a high state density on the Fermi surface, and therefore has a high carrier mobility and a low thermal mobility. This bulk semiconductor material is also easy to dope into layers. However, it is very difficult to further increase the heat transfer efficiency of this bulk semiconductor, and since a rare metal is used, there is a need for a highly efficient thermoelectric conversion element that uses another material or substitutes it from the viewpoint of the amount of resources. Yes.

  According to a first aspect of the present invention, a thermoelectric conversion element comprising: a semiconductor material that is a thermoelectric conversion material; at least one nanowire that is electrically connected to the semiconductor material; and an electrode that is electrically connected to the nanowire. Is provided. The nanowire has a semiconductor substrate and a dopant attached to the surface of the semiconductor substrate.

  According to a second aspect of the present invention, an insulating magnetic material, at least one nanowire containing a magnetic material magnetically connected to the magnetic material, and an electrode magnetically connected to the nanowire, A thermoelectric conversion element is provided.

  According to a third aspect of the present invention, there is provided a thermoelectric conversion module in which a plurality of thermoelectric conversion elements described in the first viewpoint or the second viewpoint are arranged.

  According to the fourth aspect of the present invention, the step of supplying the catalyst on the electrode, the step of disposing the semiconductor material above the electrode, and the nanowire from the catalyst so that the tip of the nanowire is joined or contacted with the semiconductor material. There is provided a method of manufacturing a thermoelectric conversion element including a growing step and a step of attaching a dopant to the surface of a nanowire.

  According to a fifth aspect of the present invention, a step of forming a magnetic body, a step of forming a nanowire precursor layer on the magnetic body, a step of forming an electrode on the nanowire precursor layer, and oxidizing the nanowire precursor layer Forming at least one nanowire, and a method for manufacturing a thermoelectric conversion element.

  The present invention has at least one of the following effects.

  In the thermoelectric conversion element of the present invention, nanowires are used for bonding the electrode and the semiconductor material or magnetic material. Thereby, thermal conductivity can be reduced and thermoelectric conversion efficiency can be improved.

  In the thermoelectric conversion element of the present invention, by joining the electrode and the semiconductor material with a nanowire, atomic diffusion between the metal and the semiconductor can be suppressed, and the conductivity of carriers from the electrode to the semiconductor material can be increased. Thereby, thermoelectric conversion efficiency can be improved.

  In the thermoelectric conversion element of the present invention, the conductivity of the spin from the electrode to the magnetic body can be increased by joining the electrode and the magnetic body with a nanowire. Thereby, thermoelectric conversion efficiency can be improved.

  According to the method for manufacturing a thermoelectric conversion element of the present invention, the thermoelectric conversion element can be easily manufactured.

1 is a schematic plan view of a thermoelectric conversion element according to a first embodiment of the present invention. The schematic diagram of a nanowire. The schematic diagram of the density of states of electrons when the nanowire of the thermoelectric conversion element has a quasi-one-dimensional structure. The schematic diagram of the density of states of electrons when the nanowire of the thermoelectric conversion element has a quasi-one-dimensional structure. The enlarged schematic plan view of nanowire. 1 is a schematic perspective view of a thermoelectric conversion module according to a first embodiment of the present invention. FIG. 7 is a schematic partial plan view of the thermoelectric conversion module shown in FIG. 6. The schematic process drawing for demonstrating the manufacturing method of the thermoelectric conversion element which concerns on 1st Embodiment of this invention. The schematic perspective view at the time of making a dopant adsorb | suck. The schematic diagram by which a carrier is introduce | transduced from an electrode to nanowire. 1 is a schematic plan view of a thermoelectric conversion element according to a first embodiment of the present invention. The schematic process drawing for demonstrating the manufacturing method of the thermoelectric conversion element which concerns on 2nd Embodiment of this invention. The schematic diagram when a spin current is introduce | transduced into an nanowire from an electrode.

  Embodiments of the present invention will be described below with reference to the drawings.

  The thermoelectric conversion element according to the first embodiment of the present invention will be described. In FIG. 1, the schematic plan view of the thermoelectric conversion element which concerns on 1st Embodiment of this invention is shown. FIG. 2 shows a schematic diagram of the nanowire.

  The thermoelectric conversion element 1 of the present invention includes an n-type semiconductor material 2, a p-type semiconductor material 3, a first electrode 8 and a second electrode 9 electrically connected to both ends of the n-type semiconductor material 2, and a p-type. The third electrode 10 and the fourth electrode 11 electrically connected to both ends of the semiconductor material 3 and the n-type semiconductor material 2 and the first electrode 8 and the second electrode 9 are arranged, and these are electrically connected. At least one first nanowire 4 and second nanowire 5 to be connected, and at least one third nanowire disposed between the p-type semiconductor material 3 and the third electrode 10 and the fourth electrode 11 to electrically connect them. A nanowire 6 and a fourth nanowire 7, a high temperature portion 12 thermally connected to the first electrode 8 and the third electrode 10, and a low temperature portion 13 thermally connected to the second electrode 9 and the fourth electrode 11. .

  As the n-type semiconductor material 2 and the p-type semiconductor material 3, a semiconductor material that can be used as a thermoelectric conversion material can be used. For example, a BiTe-based material or a PbTe-based material can be used.

  The 1st-4th nanowires 4-7 have the semiconductor base material 21 which has a linear structure (quasi one-dimensional structure), and the dopant 22 adhering to the surface. Here, “pseudo one-dimensional” means the number of dimensions in which a long distance direction is secured in the electron conduction direction. That is, “pseudo one-dimensional” means that the length in the direction connecting the semiconductor materials 2 and 3 and the electrodes 8 to 11 (the length of one nanowire) is the size in the vertical direction (the diameter of one nanowire). It means that it is very large with respect to the corresponding size. For example, the length of the first to fourth nanowires 4 to 7 is preferably 100 nanometers to 1000 nanometers. The thickness of the first to fourth nanowires 4 to 7 is preferably 1 nanometer or more and 100 nanometers or less, and more preferably 1 nanometer or more and 10 nanometers or less. Since the effect of this invention will become difficult to be acquired when a diameter exceeds 100 nanometer, it is preferable in it being 100 nanometer or less.

  Although the 1st-4th nanowires 4-7 have electroconductivity by the dopant 22, it is preferable when the heat conductivity has a property far smaller than a metal nanowire.

  It is preferable that the semiconductor substrate 21 of the first to fourth nanowires 4 to 7 does not contain a heavy metal. The heavy metal here is an element in the fifth column or less of the periodic table (that is, an element having an atomic weight equal to or higher than rubidium Rb). The materials of the first to fourth nanowires 4 to 7 include silicon (Si) material, silicon germanium (SiGe) material, gallium arsenide (GaAs) material, indium arsenide (InAs) material, and carbon (C) material. Materials etc. can be used. Examples of the carbon-based material include diamond, graphene, and carbon nanotubes. Since the carbon-based material has a high melting point and is chemically and mechanically stable even when formed in a nano-order size, the reliability as a device can be increased. Carbon nanotubes also have the advantage that they do not need to be processed to a nano-order size. Here, carbon nanotubes refer to carbon materials having a cylindrical portion, such as single wall nanotubes (SWNT), double wall nanotubes (DWNT), multiwall nanotubes (MWNT), carbon nanohorns, and the like.

  The 1st-4th nanowires 4-7 have the dopant 22 for giving the function as a semiconductor on the surface of the semiconductor base material 21. In the case of an n-type semiconductor, a charge supply type dopant 22 is attached to the nanowire. In the case of a p-type semiconductor, a charge absorbing dopant 22 is attached to the nanowire. In general, the surface of the grown nanowire includes defects / disturbances 21a. Therefore, phonon conduction is greatly reduced by surface defects / disturbances 21a (see Non-Patent Document 3). Further, in addition to this, by adsorbing the dopant molecules randomly so as to disturb the periodic structure, the heat conduction due to phonons can be greatly suppressed without greatly reducing the carrier conduction of electrons and holes. The defect / disturbance 21a refers to an atomic defect or a disorder of the atomic structure on the nanowire surface.

  As the dopant 22 that imparts semiconductor performance to the first to fourth nanowires 4 to 7, it is preferable to use an element close to the atomic number of the constituent element of the semiconductor substrate 21. As the dopant 22, for example, a hydrocarbon organic compound can be used. As a dopant for forming the first nanowire 4 and the second nanowire 5 that are n-type semiconductors, a charge supply dopant, for example, tetrathiafulvalene (TTF) can be used. As a dopant for forming the 3rd nanowire 6 and the 4th nanowire 7 which are p-type semiconductors, a charge absorption type dopant, for example, tetracyanoquinodimethane (TCNQ; tetracyanoquinodimethane) can be used.

  It is preferable to adjust the dopant amount in the first to fourth nanowires 4 to 7 so that the Fermi level of the first to fourth nanowires 4 to 7 is at or near the peak of the state density. . 3 and 4 are schematic diagrams showing the density of states of electrons when the nanowires 4 to 7 of the thermoelectric conversion element 1 shown in FIG. 1 have a quasi-one-dimensional structure. Looking at the energy state density of electrons shown in FIG. 3, a material having a one-dimensional band dispersion has a peak in the state density for a certain energy level. When this material is doped with impurities, as shown in FIG. 4, the position of the Fermi level often crosses the point where the density of states is maximized depending on the doping concentration. In the case of n-type doping, the Seebeck coefficient S in Equation 2 is increased by an order of magnitude when the Fermi level is present where the density of states of electrons (holes in the case of p-type doping) is maximized. . According to the ideal theoretical calculation, it can be increased by two orders of magnitude, but in the actual material, when the density of states of the Fermi level increases, the atomic configuration constituting the crystal of the semiconductor part spontaneously changes and the density of states Increase is suppressed to an order of magnitude.

  The degree of doping of the dopant 22 into the semiconductor substrate 21 is preferably limited to the surface of the semiconductor substrate 21. That is, it is preferable not to inject the dopant 22 into the semiconductor substrate 21. Moreover, it is preferable that the dopant 22 is not arranged with periodicity on the surface of the semiconductor substrate 21. That is, it is preferable that the dopant 22 is randomly attached to the surface of the semiconductor substrate 21.

  In the first to fourth nanowires 4 to 7, whether or not the dopant 22 is irregularly attached can be determined by measuring the electron diffraction of the surfaces of the first to fourth nanowires 4 to 7. . For example, it is preferable that no pattern is detected on the electron diffraction diffraction imaging screen. In this case, it is shown that the dopant 22 adheres to the surface of the semiconductor material without periodicity. Therefore, it is preferable that the dopant 22 is adhered to the semiconductor material so that the pattern is not detected on the electron diffraction diffraction imaging screen.

  Even if the dopant 22 is only attached to the surface of the semiconductor substrate 21, since the width of the semiconductor substrate 21 is on the order of nanometers, carriers (holes or electrons) penetrate into the semiconductor substrate 21. can do. Thereby, the first to fourth nanowires 4 to 7 have semiconductor properties.

  The first electrode and the second electrode are conductive materials. As the first electrode and the second electrode, for example, aluminum, copper, or the like can be used.

The high-temperature part 12 and the low-temperature part 13 cause the nanowires 4 to 7 and the semiconductor materials 2 to 3 to have a temperature gradient. For example, a heating device (not shown) is connected to the high temperature section 12. For example, a cooling device (not shown) is connected to the low temperature part 13. The high temperature part 12 and the low temperature part 13 are insulating materials, and an electromotive force is lost when a current flows through the high temperature part 12 and the low temperature part 13, so that the high temperature part 12 and the low temperature part 13 have a large band gap. Is preferable. As the high temperature part 12 and the low temperature part 13, for example, a glass material such as SiO ₂ can be used.

  FIG. 5 shows an enlarged schematic plan view of nanowires in the thermoelectric conversion element. The thermoelectric conversion element 1 includes a catalyst 31 interposed between the first to fourth electrodes 8 to 11 and the first to fourth nanowires 4 to 7, the first to fourth electrodes 8 to 11, and the first to fourth. It is preferable to further include a resistance reducing agent 32 disposed around the contact with the nanowires 4 to 7.

  The catalyst 31 is used for growing the first to fourth electrodes 8 to 11. As the catalyst 31, fine particles such as gold, nickel, platinum, and aluminum can be used when a semiconductor material is grown. When growing carbon nanotubes, fine particles of iron can be used.

  The resistance lowering agent 32 reduces the contact resistance between the first and fourth electrodes 8 to 11 to the first to fourth nanowires 4 to 7 and reduces the contact resistance between them. It enhances sex. As the resistance reducing agent 32 in the n-type first electrode 8 and the second electrode 9, a substance that facilitates electron injection, for example, metal fine particles such as potassium (K) and calcium (Ca) can be used. As the resistance lowering agent 32 in the p-type third electrode 10 and the fourth electrode 11, a substance that facilitates hole injection, such as fullerene or pentacene, can be used.

  Next, the thermoelectric conversion module according to the first embodiment of the present invention will be described. FIG. 6 shows a schematic perspective view of the thermoelectric conversion module according to the first embodiment of the present invention. FIG. 7 shows a schematic partial plan view of the thermoelectric conversion module shown in FIG. 6 and 7, the same elements as those shown in FIG. 1 are denoted by the same reference numerals.

  The thermoelectric conversion module 100 basically has a configuration in which the thermoelectric conversion elements 1 shown in FIG. 1 are arranged in parallel. That is, an n-type unit composed of the first nanowire 4, the n-type semiconductor material 2 and the second nanowire 5, and a p-type unit composed of the third nanowire 6, the p-type semiconductor material 3 and the fourth nanowire 7, Are arranged alternately. In the thermoelectric conversion unit 1 shown in FIG. 1, each electrode does not electrically connect adjacent units, but in the thermoelectric conversion module 100, each electrode electrically connects adjacent units. . The first electrode 41 electrically connects the n-type unit and the p-type unit on the high temperature part 12 side. That is, the first electrode 41 is electrically connected to the n-type semiconductor material 2 via the first nanowire 4 and is electrically connected to the p-type semiconductor material 3 via the third nanowire 6. The second electrode 42 electrically connects the p-type unit and the n-type unit on the low temperature part 13 side. That is, the second electrode 42 is electrically connected to the p-type semiconductor material 3 through the fourth nanowire and is electrically connected to the n-type semiconductor material 2 through the second nanowire 5. The first electrode 41 and the second electrode 42 are arranged alternately. That is, when the first electrode 41 and the second electrode 42 are connected to the same n-type unit, the first electrode 41 and the second electrode 42 are connected to different p-type units. Similarly, when the first electrode 41 and the second electrode 42 are connected to the same p-type unit, the first electrode 41 and the second electrode 42 are connected to different n-type units. Although the high temperature part 12 and the low temperature part 13 may be provided for each electrode as shown in FIG. 1, in the form shown in FIGS. 6 and 7, the high temperature part 12 is a substrate common to the plurality of first electrodes 41. The low temperature part 13 is configured as a substrate common to the plurality of second electrodes 42.

  According to the thermoelectric conversion module 100, high-density mounting is possible, and the acquired voltage can be increased.

  Next, the manufacturing method of the thermoelectric conversion element which concerns on 1st Embodiment of this invention is demonstrated. In FIG. 8, the schematic process drawing for demonstrating the manufacturing method of the thermoelectric conversion element which concerns on 1st Embodiment of this invention is shown.

  First, first to fourth electrodes 8 to 11 are prepared. Next, the catalyst 31 necessary for the growth of the nanowires 4 to 7 is disposed on each of the electrodes 8 to 11. Next, the semiconductor materials 2 to 3 are arranged on the electrodes 8 to 11 so as to be separated from the electrodes 8 to 11 by a length for growing the nanowires 4 to 7 (FIG. 8A).

  Next, nanowires 4 to 7 are grown from the catalyst 31. For example, the nanowires 4 to 7 are grown by gas spraying 33 using a technique such as a chemical vapor deposition method (CVD (Chemical Vapor Deposition) method) or a VLS (Vapor-Liquid-Solid) method. At this time, the growth direction of the nanowires 4 to 7 is controlled by applying the electric field 34. The grown nanowires 4 to 7 are bonded or brought into contact with the semiconductor materials 2 to 3, and the nanowires 4 to 7 and the semiconductor materials 2 to 3 are electrically connected (FIG. 8B). The nanowires 4 to 7 may be grown on both sides of the semiconductor materials 2 to 3 simultaneously, or may be grown on one side.

  Next, the resistance reducing agent 32 is adsorbed around the joint between the electrodes 8 to 11 and the nanowires 4 to 7 (FIG. 8C). In the form shown in FIG. 8, the resistance reducing agent 32 is applied after the nanowires 4 to 7 are grown. However, the nanowires 4 to 7 may be grown after the resistance reducing agent 32 is applied.

  Next, the dopant 22 is adsorbed on the nanowires 4 to 7. FIG. 9 shows a schematic perspective view when adsorbing the dopant. An isolation wall 35 is formed between the n-type unit and the p-type unit in which the electrodes 8 to 11 and the semiconductor materials 2 to 3 are connected via the nanowires 4 to 7. The isolation wall 35 prevents both the n-type dopant and the p-type dopant from adhering to the nanowire when supplying the dopant to the nanowires 4 to 7. After the isolation wall 35 is formed, the step of adsorbing the n-type dopant on the first nanowire 4 and the second nanowire 5 and the step of adsorbing the p-type dopant on the third nanowire 6 and the fourth nanowire 7 are performed separately. carry out. By providing the isolation wall 35, the p-type dopant is prevented from adhering to the first nanowire 4 and the second nanowire 5, and the n-type dopant is adhered to the third nanowire 6 and the fourth nanowire 7. To prevent.

  The isolation wall 35 preferably has insulating properties and low thermal conductivity. As the isolation wall 35, a glass material, silicon oxide, or the like can be used. Thereby, for example, when producing a module like FIG. 6, the short circuit between thermoelectric conversion elements can be prevented.

  The amount of adsorbed dopant is preferably adjusted so that the Fermi level matches the peak position of the state density while performing optical absorption measurement of the semiconductor portion. A quasi-one-dimensional nanowire has a peak specific to the one-dimensional system in the density of states. By introducing the amount of molecular dopant into the nanowire so that the density of states reaches the maximum peak, the flow of electrons and holes can be increased, and the conductivity of carriers can be improved. Become. Accordingly, the amount of adsorbed dopant is adjusted by the disappearance of the light absorption peak that appears when shifting from the peak position of the occupied portion of the state density to the peak position of the unoccupied portion in the light absorption measurement of the semiconductor portion.

  According to the said manufacturing method, a thermoelectric conversion element can be manufactured by a simple method.

  Next, the operation of the thermoelectric conversion element 1 according to the first embodiment of the present invention will be described. FIG. 10 shows a schematic diagram in which carriers are introduced from the electrode into the nanowire. In FIG. 10, the area | region of the electrodes 8-11 has shown the electronic state in an electrode typically. The region of the junction between the electrodes 8-11 and the nanowires 4-7 illustrates the energy barrier against carriers. The regions of nanowires 4-7 illustrate the density of states with respect to energy.

  In order to generate electric power in the thermoelectric conversion element 1, the first electrode 8 and the third electrode 10 are set to a high temperature, the second electrode 9 and the fourth electrode are set to a lower temperature than the first electrode 8 and the third electrode 10, and the n-type semiconductor A temperature gradient is generated in the material 2, the p-type semiconductor material 3, and the first to fourth nanowires 4 to 7. As a result, carrier transfer of electrons and holes and heat conduction in thermal diffusion are caused.

  One of the causes of hindering heat conduction and electron / hole carrier mobility in a thermoelectric conversion element is a junction between an electrode and a semiconductor material that require heterojunction. In particular, it is important to reduce the electrical resistance and increase the electrical conductivity at the junction between the electrode and the semiconductor material. Therefore, in the thermoelectric conversion element 1 of the present invention, the atomic diffusion of metal atoms and semiconductor atoms is suppressed by joining the electrodes 8 to 11 and the semiconductor materials 2 to 3 with the nanowires 4 to 7. Moreover, carrier conductivity is improved by supplying the resistance reducing agent 32 to the junction part of the electrodes 8-11 and the nanowires 4-7. That is, the energy barrier at the junction with respect to the carrier is lowered.

  Furthermore, the nanowires 4 to 7 form semiconductor nanowires by the dopant 22 adhering to the surface of the semiconductor substrate 21, and the thermal conduction is reduced by the phonon scattering effect with the surface adsorbed molecules. That is, the nanowires 4 to 7 reduce the thermal conductivity from the electrodes 8 to 11 to the semiconductor materials 2 to 3.

  Regarding the carrier conduction by electrons and holes, the energy band number of electrons and holes decreases in the conduction band and valence band, but the energy change (band dispersion) with respect to the wave number change of electrons and holes is more than the band dispersion of phonons. Because it is large, the decrease in carrier conductivity is small with respect to the decrease in dimension. If the dopant 22 is only attached to the surface of the semiconductor substrate 21, carriers are released, and the charged dopant 22 exists only on the surface of the semiconductor substrate 21. Thereby, the influence which the charged dopant 22 inhibits the movement 23 of an electron and a hole can be reduced. That is, the mobility of electrons and holes inside the semiconductor substrate 21 is difficult to be reduced by the charged dopant 22 present on the surface. Therefore, the Seebeck coefficient S determined by the electron / hole carrier conductivity is not greatly reduced.

  Regarding the heat conduction, in the first to fourth nanowires 4 to 7 having a quasi-one-dimensional structure, as the diameters of the first to fourth nanowires 4 to 7 become smaller, the thermal conductivity κ (the above formula 2) greatly decreases. As a result, the thermoelectric figure of merit ZT greatly increases (see Non-Patent Document 3). Here, the reason why the thermal conductivity κ is lowered in the quasi-one-dimensional structure is that the vibration mode of the lattice vibration of the material that is a medium responsible for the propagation of heat is reduced, so that the phonon of thermal conduction is reduced.

  Phonon conduction is greatly affected by structural changes and disturbances on the surfaces of the first to fourth nanowires 4 to 7, and the conduction is lowered. The acoustic phonon responsible for heat conduction propagates on the outer surfaces of the first to fourth nanowires 4 to 7 as indicated by an arrow 24 shown in FIG. In general, when a molecule that is an n-type dopant or a molecule that is a p-type dopant is attached in an amount until the Fermi level changes to the peak position of the density of states as shown in FIG. An average of one molecule is attached in the range of. An acoustic phonon can be moved ballistically over a distance of 1000 km with a normal material on a clean surface, but since the ballistic distance is reduced to 50 mm, the conductivity κ can be estimated to be reduced to about 1/20. . Therefore, if the dopant 22 is irregularly attached to the surfaces of the first to fourth nanowires 4 to 7, the periodic structure formed by the lattice is disturbed, so that acoustic phonons are scattered and the propagation speed is significantly reduced. It will be.

  From the above, the thermoelectric conversion efficiency can be increased by the first to fourth nanowires 4 to 7.

  Next, a thermoelectric conversion element according to the second embodiment of the present invention will be described. In FIG. 11, the schematic plan view of the thermoelectric conversion element which concerns on 2nd Embodiment of this invention is shown.

  The thermoelectric conversion element 51 according to the second embodiment includes a magnetic body 52, a first nanowire 53 magnetically connected to one end of the magnetic body 52, and a magnetic end at the other end of the magnetic body 52. The connected second nanowire 54, the first electrode 55 magnetically connected to the first nanowire 53, the second electrode 56 magnetically connected to the second nanowire 54, and the first electrode 55 thermally. And a low temperature part 58 thermally connected to the second electrode 56. The magnetic body 52 and the first electrode 55 are magnetically connected via the first nanowire 53. The magnetic body 52 and the second electrode 56 are magnetically connected via the second nanowire 54.

  In the present invention, being magnetically connected means having an interaction between spins. In the present invention, magnetism refers to the property of ordering in the spin arrangement due to the interaction between spins.

  The magnetic body 52 is preferably a material having low thermal conductivity, for example, an insulator. As the magnetic body 52, a ferromagnetic body (ferromagnetic body) or a ferrimagnetic body can be used, and it is desirable to use a material having low thermal conductivity and small spin current relaxation. As the magnetic body 52, for example, an oxide-based magnetic body such as garnet ferrite or spinel ferrite can be used. In particular, if a polycrystalline or nanocrystalline magnetic material 52 is used, phonon thermal conduction can be suppressed by effective phonon scattering, and higher sensitivity and resolution can be obtained.

  The first electrode 55 and the second electrode 56 preferably contain a material having a spin orbit interaction in order to extract a thermoelectromotive force from the spin current by the reverse spin Hall effect. As the electrodes 55 and 56, for example, a metal material such as Au, Pt, or Pd having a relatively large spin-orbit interaction or an alloy material containing such a metal material can be used. The electrodes 55 and 56 may contain impurities such as Fe and Cu in order to enhance the reverse spin Hall effect. The thicknesses of the electrodes 55 and 56 are preferably set to at least the spin diffusion length of the metal material in order to convert the spin current into electricity with high efficiency. For example, when the electrode is formed of Au, the thickness of the electrode is preferably set to 50 nm or more. When the electrode is formed of Pt, the thickness is preferably set to 10 nm or more.

  The first nanowire 53 and the second nanowire 54 are magnetic materials. The first nanowire 53 and the second nanowire 54 contain a magnetic material having magnetization in at least one direction, for example, a ferromagnetic material (ferromagnetic material) or a ferrimagnetic material. As the nanowires 53 and 54, for example, a metal material such as iron or nickel or an insulator material such as spinel ferrite can be used.

  The nanowires 53 and 54 have a linear structure (pseudo one-dimensional structure). For example, the length of the nanowires 53 and 54 is preferably 100 nanometers to 1000 nanometers. The thickness of the nanowires 53 and 54 is a thickness that can secure a propagation path of magnon, for example, preferably 1 nm or more and 100 nm or less, and more preferably 1 nm or more and 10 nm or less. .

  A resistance lowering agent that increases the spin conductivity may be applied to the junction between the nanowires 53 and 54 and the electrodes 55 and 56.

  Next, the manufacturing method of the thermoelectric conversion element which concerns on 2nd Embodiment of this invention is demonstrated. In FIG. 12, the schematic process drawing for demonstrating the manufacturing method of the thermoelectric conversion element which concerns on 2nd Embodiment of this invention is shown.

  First, a substrate 61 that supports a thermoelectric conversion element is prepared. For example, a gadolinium gallium garnet (hereinafter referred to as “GGG”) substrate having a thickness of 0.5 mm can be used.

Next, the magnetic body 52 is formed on the substrate 61. The magnetic body 52 can be formed, for example, by a method such as an organic metal deposition method (MOD (Metal Organic Deposition) method), a sol-gel method, an aerosol deposition method (AD (Aerosol Deposition) method). If a coating / printing-based film forming method is used, it is possible to form a film on a large area substrate in a lump, and manufacturing with high productivity becomes possible. For example, a magnetic substance 52 containing yttrium iron garnet (composition BiY ₂ Fe ₅ O _12, hereinafter referred to as “Bi-YIG”) in which a part of yttrium (Y) site is substituted with Bi on a GGG substrate is aerosolized. It can be deposited by the deposition method. Bi-YIG fine particles having a diameter of 300 nm can be used as the Bi-YIG raw material. The Bi-YIG fine particles are packed in an aerosol generation container, and the GGG substrate is fixed to a holder in the film forming chamber. In this state, a pressure difference is generated between the film forming chamber and the aerosol generating container, whereby Bi-YIG fine particles are drawn into the film forming chamber and sprayed onto the GGG substrate through the nozzle. The fine particles are crushed and recombined by the collision energy at the substrate at this time, and Bi-YIG polycrystal is formed on the GGG substrate. By scanning the substrate stage two-dimensionally, a uniform Bi-YIG magnetic body 52 layer can be formed on the substrate with a film thickness of, for example, 0.1 mm.

  The nanowires 53 and 54 can be produced, for example, by an electrochemical method, thermal oxidation under appropriate conditions, or the like.

  The electrodes 55 and 56 can be manufactured by a method such as sputtering or vapor deposition. Further, it can be manufactured by a highly productive manufacturing method such as an ink jet method or a screen printing method.

For example, after polishing the surface of the Bi-YIG 52, an Fe layer having a thickness of 1 μm to be the nanowire precursor layer 62 is first formed on the Bi-YIG 52 by sputtering. Next, a Pt layer having a thickness of 30 nm to be the electrodes 55 and 56 is formed on the Fe layer 62 by sputtering. Next, these layers are annealed in an oxygen atmosphere at a high temperature of 500 ° C. for 5 hours, whereby the Fe layer is oxidized and nanostructured. The Bi-YIG and the Pt layer have a diameter of 50 nm and a length of 1 μm. A large number of hematite (α-Fe ₂ O ₃ ) nanowires 53 and 54 can be formed. The nanowire precursor layer 62 may be formed on both ends of the magnetic body 52 and then thermally oxidized, or the nanowires 53 and 54 may be formed on each side of the magnetic body 52.

  According to the above method, nanowires that are magnetically connected magnetic materials can be easily produced.

  Next, the operation of the thermoelectric conversion element 51 according to the second embodiment of the present invention will be described. In the thermoelectric conversion element 51, an electromotive force is generated by a spin Seebeck effect by a spin current. In the Seebeck effect by the spin current, the upward spin and the downward spin flowing through the magnetic body 52 and the nanowires 53 and 54 correspond to electrons of the n-type semiconductor material and holes of the p-type semiconductor material in the first embodiment. The spin current is converted into an electron system by the reverse spin Hall effect using the spin-orbit interaction in the electrodes 55 and 56. The spin current has an extremely large mean free path of about 1 cm and does not cause scattering or relaxation, so that no heat is generated in the magnetic body 52. Therefore, as a factor for increasing the thermoelectric conversion efficiency, in order to maintain the temperature difference between the high temperature portion 57 and the low temperature portion 58, there is a reduction in heat conduction by phonons flowing through the electrodes 55 and 56 and the magnetic body 52. Therefore, in the thermoelectric conversion element 51, phonon conduction is suppressed by forming nanowires 53 and 54 between the electrodes 55 and 56 and the magnetic body 52. That is, when the nanowires 53 and 54 are magnetic materials, the spin conduction is transmitted through the spin channel without being greatly scattered. Thereby, it becomes possible to increase the thermoelectric conversion efficiency by forming the nanowires 53 and 54 between the electrodes 55 and 56 and the magnetic body 52.

  FIG. 13 shows a schematic diagram when the spin current is introduced from the electrode to the nanowire. In the nanowires 53 and 54, the conduction band through which the upward spin passes (upper Hubbard band) and the conduction band through which the downward spin passes (lower Hubbard band) are split due to the Coulomb repulsion interaction between the electrons that generate spin. is doing. If the overlap between the state density of the electrode and the state density of the conduction band of the nanowire can be increased, the conductivity of the spin current can be improved.

  The nanowires 53 and 54 increase the thermoelectric conversion efficiency by reducing the thermal conductivity between the electrodes 55 and 56 and the magnetic body 52 in the same manner as in the first embodiment.

  According to the present embodiment, unlike the first embodiment, two types of basic elements are not required unlike the n-type unit and the p-type unit. Thereby, a thermoelectric conversion element can be efficiently formed with respect to a required area. In addition, when the amount of power generation is increased, it is not necessary to combine a plurality of thermoelectric conversion elements as in the thermoelectric conversion module shown in FIG. 6, and it is easy to increase the area, and only the junction area between the electrode and the magnetic material is increased. The amount of power generation can be increased.

  The thermoelectric conversion element and the manufacturing method thereof according to the present invention have been described based on the above embodiment, but are not limited to the above embodiment, and are within the scope of the present invention and within the basic technical idea of the present invention. It goes without saying that various modifications, changes and improvements can be included in the above embodiment. Further, various combinations, substitutions, or selections of various disclosed elements are possible within the scope of the claims of the present invention.

  Further problems, objects, and developments of the present invention will become apparent from the entire disclosure of the present invention including the claims.

  A part or all of the above embodiment may be described as in the following supplementary notes, but is not limited to the following description.

(Appendix 1)
A semiconductor material that is a thermoelectric conversion material;
At least one nanowire electrically connected to the semiconductor material;
An electrode electrically connected to the nanowire,
The nanowire includes a semiconductor base material and a dopant attached to the surface of the semiconductor base material.

(Appendix 2)
The thermoelectric conversion element according to appendix 1, further comprising a resistance lowering agent that reduces an electrical resistance between the nanowire and the electrode at a joint between the nanowire and the electrode.

(Appendix 3)
An n-type semiconductor material and a p-type semiconductor material as the semiconductor material,
As the nanowire, at least one first nanowire electrically connected to one end of the n-type semiconductor material, and at least one first wire electrically connected to the other end of the n-type semiconductor material. Two nanowires, at least one third nanowire electrically connected to one end of the p-type semiconductor material, and at least one first electrically connected to the other end of the p-type semiconductor material. 4 nanowires,
As the electrodes, a first electrode electrically connected to the first nanowire, a second electrode electrically connected to the second nanowire, and a third electrode electrically connected to the third nanowire And a fourth electrode electrically connected to the fourth nanowire. The thermoelectric conversion element according to appendix 1 or 2, characterized by comprising:

(Appendix 4)
The junction between the first nanowire and the first electrode and the junction between the second nanowire and the second electrode have an electrical resistance between the first nanowire and the first electrode, and the second nanowire and the first electrode. It further comprises a resistance reducing agent that reduces the electrical resistance with the two electrodes,
The thermoelectric conversion element according to appendix 3, wherein the resistance reducing agent contains at least one of calcium and potassium.

(Appendix 5)
The junction between the third nanowire and the third electrode and the junction between the fourth nanowire and the fourth electrode are connected to the electrical resistance of the third nanowire and the third electrode, and the fourth nanowire and the fourth electrode. A resistance reducing agent that lowers the electrical resistance with the four electrodes;
The thermoelectric conversion element according to appendix 3 or 4, wherein the resistance lowering agent contains at least one of fullerene and pentacene.

(Appendix 6)
The thermoelectric conversion element according to any one of appendices 1 to 5, wherein the Fermi level of each nanowire is at the peak of the state density.

(Appendix 7)
Each nanowire has a structure in which the carrier conduction direction becomes a quasi-one-dimensional direction, The thermoelectric conversion element according to any one of Supplementary notes 1 to 6, wherein

(Appendix 8)
The thermoelectric conversion element according to any one of appendices 1 to 7, further comprising an isolation wall between the nanowires of different conductivity types and between the semiconductor materials.

(Appendix 9)
An insulating magnetic material;
At least one nanowire containing a magnetic material magnetically connected to the magnetic body;
An electrode magnetically connected to the nanowire;
A thermoelectric conversion element comprising:

(Appendix 10)
As the nanowire, at least one first nanowire magnetically connected to one end of the magnetic body, and at least one second nanowire magnetically connected to the other end of the magnetic body, With
The thermoelectric conversion according to appendix 9, wherein the electrode includes a first electrode magnetically connected to the first nanowire and a second electrode magnetically connected to the second nanowire. element.

(Appendix 11)
The thermoelectric conversion element according to appendix 9 or 10, wherein each nanowire has a structure in which a spin conduction direction is a quasi-one-dimensional direction.

(Appendix 12)
The thickness of each nanowire is 1 nanometer-1000 nanometer, The thermoelectric conversion element as described in any one of the supplementary notes 1-11 characterized by the above-mentioned.

(Appendix 13)
A thermoelectric conversion module, wherein a plurality of the thermoelectric conversion elements according to any one of appendices 1 to 12 are arranged.

(Appendix 14)
14. The thermoelectric conversion module according to appendix 13, wherein at least one electrode is shared between at least one pair of adjacent thermoelectric conversion elements.

(Appendix 15)
Supplying a catalyst on the electrode;
Disposing a semiconductor material above the electrode; and
Growing the nanowire from the catalyst such that the tip of the nanowire is bonded or in contact with the semiconductor material;
Attaching a dopant to the surface of the nanowire;
The manufacturing method of the thermoelectric conversion element characterized by including this.

(Appendix 16)
The method of manufacturing a thermoelectric conversion element according to appendix 15, further comprising a step of supplying a resistance lowering agent that lowers an electrical resistance between the nanowire and the electrode to a joint between the nanowire and the electrode.

(Appendix 17)
The method for producing a thermoelectric conversion element according to appendix 15 or 16, further comprising a step of forming an isolation wall between nanowires supplying different dopants.

(Appendix 18)
18. The method for manufacturing a thermoelectric conversion element according to appendix 17, wherein the isolation wall has an insulating property.

(Appendix 19)
In the step of attaching a dopant to the surface of the nanowire,
The method for producing a thermoelectric conversion element according to any one of appendices 15 to 18, wherein the dopant is attached so that the Fermi level is a peak position of the state density.

(Appendix 20)
Forming a magnetic material;
Forming a nanowire precursor layer on the magnetic material;
Forming an electrode on the nanowire precursor layer;
Oxidizing the nanowire precursor layer to form at least one nanowire;
The manufacturing method of the thermoelectric conversion element characterized by including this.

  The thermoelectric conversion element and the thermoelectric conversion module of the present invention can be reused, for example, as a power source for waste heat discharged from electronic devices such as personal computers and mobile phones, power supply elements for wearable electronic devices and sensors, and nighttime solar cells. It can be used as a standby power source that complements the above, a heater that uses a temperature difference between indoor and outdoor in a cold region, and a thermoelectric conversion device in a lithium battery electrical system that generates high heat.

DESCRIPTION OF SYMBOLS 1 Thermoelectric conversion element 2 N-type semiconductor material 3 P-type semiconductor material 4-7 1st-4th nanowire 8-11 1st-4th electrode 12 High temperature part 13 Low temperature part 21 Semiconductor base material 21a Surface defect and disorder 22 Dopant 23 Electron or hole flow 24 Phonon flow 31 Catalyst 32 Resistance reducing agent 33 Gas flow 34 Electric field 35 Separating wall 41 First electrode 42 Second electrode 51 Thermoelectric conversion element 52 Magnetic body 53, 54 First to second nanowire 55, 56 First and second electrodes 57 High temperature part 58 Low temperature part 61 Substrate 62 Nanowire precursor layer 100 Thermoelectric conversion module

Claims (10)

A semiconductor material that is a thermoelectric conversion material;
At least one nanowire electrically connected to the semiconductor material;
An electrode electrically connected to the nanowire,
The nanowire includes a semiconductor base material and a dopant attached to the surface of the semiconductor base material.   The thermoelectric conversion element according to claim 1, further comprising a resistance lowering agent that reduces an electrical resistance between the nanowire and the electrode at a joint between the nanowire and the electrode. An n-type semiconductor material and a p-type semiconductor material as the semiconductor material,
As the nanowire, at least one first nanowire electrically connected to one end of the n-type semiconductor material, and at least one first wire electrically connected to the other end of the n-type semiconductor material. Two nanowires, at least one third nanowire electrically connected to one end of the p-type semiconductor material, and at least one first electrically connected to the other end of the p-type semiconductor material. 4 nanowires,
As the electrodes, a first electrode electrically connected to the first nanowire, a second electrode electrically connected to the second nanowire, and a third electrode electrically connected to the third nanowire The thermoelectric conversion element according to claim 1, further comprising: a fourth electrode electrically connected to the fourth nanowire. An insulating magnetic material;
At least one nanowire containing a magnetic material magnetically connected to the magnetic body;
An electrode magnetically connected to the nanowire;
A thermoelectric conversion element comprising: As the nanowire, at least one first nanowire magnetically connected to one end of the magnetic body, and at least one second nanowire magnetically connected to the other end of the magnetic body, With
5. The thermoelectric device according to claim 4, comprising a first electrode magnetically connected to the first nanowire and a second electrode magnetically connected to the second nanowire as the electrodes. Conversion element.   A thermoelectric conversion module in which a plurality of the thermoelectric conversion elements according to claim 1 are arranged. Supplying a catalyst on the electrode;
Disposing a semiconductor material above the electrodes;
Growing the nanowire from the catalyst such that the tip of the nanowire is bonded or in contact with the semiconductor material;
Attaching a dopant to the surface of the nanowire;
The manufacturing method of the thermoelectric conversion element characterized by including this.   The method of manufacturing a thermoelectric conversion element according to claim 7, further comprising a step of supplying a resistance lowering agent that reduces an electrical resistance between the nanowire and the electrode to a joint portion between the nanowire and the electrode. . In the step of attaching a dopant to the surface of the nanowire,
The method of manufacturing a thermoelectric conversion element according to claim 7 or 8, wherein the dopant is attached so that the Fermi level is a peak position of the state density. Forming a magnetic material;
Forming a nanowire precursor layer on the magnetic material;
Forming an electrode on the nanowire precursor layer;
Oxidizing the nanowire precursor layer to form at least one nanowire;
The manufacturing method of the thermoelectric conversion element characterized by including this.

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