JP6609109B2 - Thermoelectric conversion element and method for manufacturing the same, thermoelectric power generation device and Peltier device - Google Patents

Description

  The present embodiment relates to a thermoelectric conversion element, a manufacturing method thereof, a thermoelectric power generation device, and a Peltier device.

  In recent years, energy saving and efficient use of energy have become important issues in human life due to environmental problems and resource problems on a global scale. Considering that all the energy will eventually turn into heat, thermoelectric power generation that can recycle energy that has been discarded as heat is the ultimate energy recycling. For this reason, technological development and research for improving the performance of thermoelectric conversion are being promoted.

  Here, a thermoelectric conversion element using a BiTe-based material has been industrialized slightly (for example, refer to Patent Document 1). As an example of improving the performance in the BiTe system, a technique for reducing the thermal conductivity κ of a material is often used (see, for example, Non-Patent Document 1). Here, a technique has been reported in which the transmission of heat is reduced by increasing the phonon scattering by reducing the polycrystalline grain size in the material.

  In addition, material development using a skutterudite compound (for example, see Non-Patent Document 2) and a layered material (for example, Non-Patent Document 3 and Non-Patent Document 4) has been carried out. It is difficult to produce even if it is good, and it has not yet been industrialized due to reports at the basic research stage.

  A general BiTe-based thermoelectric conversion element contains Te, which is a rare metal, and Te is known to be toxic by itself. Moreover, the general use temperature at which BiTe can operate is as low as about 200 ° C., and is not suitable for use at a high temperature. In addition, since it is difficult to form a large-size crystal, there is a problem that the temperature difference between the high temperature side and the low temperature side is short and it is difficult to make a temperature difference. Moreover, since the thermoelectric conversion element is made by combining two types of n-type material and p-type material, the thermal expansion coefficients of the respective materials need to be approximately the same.

  In addition, Non-Patent Document 5 discloses a report proposed by Hicks and Dresselhaus for improving the dimensionless figure of merit ZT by “reducing the dimension of the structure”. This is a technique of increasing the phonon scattering by reducing the structure and reducing the thermal conductivity. Similarly, nanowires having a one-dimensional structure are disclosed (for example, see Non-Patent Document 6). However, although the characteristics of nanowires are drastically improved due to the effect of reducing thermal conductivity due to increased phonon scattering, the nanowires are difficult to handle and are not suitable for devices.

The approach from a low-dimensional structure that is easy to industrialize includes an approach from a two-dimensional structure that is easy to control. The approaches for reducing the thermal conductivity κ in the two-dimensional structure are PbTe / PbEuTe (non-patent document 5) having a quantum well structure, Bi ₂ Te ₃ / Sb ₂ Te ₃ (non-patent document 7) having a superlattice structure, PbSeTe / PbTe (Non-Patent Document 8), GaN / AlN / AlGaN (Non-Patent Document 9), and the like are disclosed. The Seebeck coefficient of bulk GaN is disclosed in Non-Patent Document 10.

Japanese Patent Laid-Open No. 03-16281 JP 2009-117430 A

Bed Poudel et al., “High-Thermoelectric Performance of Nanostructured Bismuth Antimony Telluride Bulk Alloys”, Science 320,634 (2008). B.C.Sales et al., “Filled Skutterudite Antimonides: A New Class of Thermoelectric Materials”, Science 272, 1325 (1996). Li-Dong Zhao et al., “Ultralow thermal conductivity and high thermoelectric figure of merit in SnSe crystals”, Nature 508,373 (2014). S. Ishiwata et al., “Extremely high electron mobility in a phonon-glass semimetal”, Nature Mater. 12, 512 (2013). L.D.Hicks et al., “Experimental study of the effect of quantum-well structures on the thermoelectric figure of merit”, Phys. Rev. B 53, R10493 (1996). Allon I. Hochbaum et al., “Enhanced thermoelectric performance of rough silicon nanowires”, Nature 451, 163 (2007). Rama Venkatasubramanian et al., “Thin-film thermoelectric devices with high room-temperature figures of merit”, Nature 413, 597 (2001). T.C.Harman et al., “Quantum Dot Superlattice Thermoelectric Materials and Devices”, Science 297, 2229 (2002). Alexander Sztein et al., “Polarization field engineering of GaN / AlN / AlGaN superlattices for enhanced thermoelectric properties”, Appl. Phys. Lett. 104, 042106 (2014). B. Kucukgok, B. Wang, A. G. Melton, N. Lu, I. T. Ferguson, “Comparison of thermoelectric properties of GaN and ZnO samples”, Phys. Stat. Sol. C11, No. 3-4, 894-897 (2014).

  However, these low-dimensional materials have problems such as using Te or low efficiency.

  On the other hand, non-patent document 5 discloses an increase in Seebeck coefficient S as another phenomenon that occurs when the dimension of the structure proposed by Hicks and Dresselhaus is reduced. This is a phenomenon in which, by confining electrons in the quantum well potential, the density of states of the electrons becomes discrete, and the Seebeck coefficient S becomes larger than that in the bulk state. However, although the Seebeck coefficient S in this quantum well is increased as compared with the Seebeck coefficient S at the same carrier concentration in the bulk, the trade-off relationship in which the Seebeck coefficient S decreases as the carrier concentration increases does not change.

As a technique for overcoming this trade-off, Patent Document 2 discloses a thermoelectric conversion element using SrTiO ₃ . This is because an insulating film made of 12CaO · 7Al ₂ O ₃ or the like is formed on SrTiO ₃ , a gate bias is applied like a metal-insulator-semiconductor field effect transistor (MISFET), and the carrier Is induced to form a two-dimensional electron gas (2DEG) layer. In 2DEG of SrTiO ₃ , by applying a high electric field of 100 MV · cm ⁻¹ or more and confining very high density electrons of 10 ¹⁴ cm ^{−2 in} the film thickness of about 2 nm, the V of Seebeck coefficient S It is disclosed that character recovery occurs. Non-patent documents 5.7, 8, and 9 do not disclose V-shaped recovery of the Seebeck coefficient S.

  In the bulk material, the Seebeck coefficient S and the electrical conductivity σ are in a trade-off relationship with the carrier concentration. Therefore, when the carrier concentration n is increased to increase the electrical conductivity σ, the Seebeck coefficient S is decreased. Conversely, if the Seebeck coefficient S is to be increased, the carrier concentration n must be lowered, resulting in a problem that the electrical conductivity σ is lowered.

As a technique for overcoming this, Patent Document 2 discloses that the Seebeck coefficient S recovers to a V-shape as the carrier concentration increases (increases the applied bias) in 2DEG formed by applying a gate bias to SrTiO _3. It is disclosed. However, in the SrTiO ₃ material system having this gate structure, since it is very difficult to stack, the electrical conductivity σ cannot be increased, and the trade-off between the Seebeck coefficient S and the electrical conductivity σ cannot be solved. There are challenges.

  The present embodiment improves the trade-off between Seebeck coefficient and carrier concentration, and the trade-off between Seebeck coefficient and electric conductivity, and can be stacked with high electric conductivity, a method for manufacturing the thermoelectric conversion element, and the thermoelectric conversion. A thermoelectric generator and a Peltier device using the element are provided.

According to one embodiment of the present embodiment, the first material layer, the second material layer disposed in contact with the first material layer, the first material layer, and the second material layer are electrically connected A connected first electrode; a second electrode electrically connected to the first material layer and the second material layer and spaced apart from the first electrode ; the first material layer; And a substrate on which a unit structure is formed by the second material layer, and an interface between the first material layer and the second material layer is between the first material layer and the second material layer. When the electric polarization is discontinuous, an electric conductive layer mainly responsible for electric conduction is generated, and the first electrode and the second electrode are electrically connected to the electric conductive layer when the electric conductive layer is generated. The electric polarization difference at the interface between the first material layer and the second material layer is Seebeck coefficient of the conductive layer is set in a relationship that increases with the increase in the reduction Fermi energy, the unit structure of the first material layer and the second material layer, the said first material layer the There is provided a thermoelectric conversion element formed over a plurality of layers so that the interface between the two material layers and the surface of the substrate are perpendicular to each other.

According to another aspect of the present embodiment, the first material layer, the second material layer disposed in contact with the first material layer, the first material layer and the second material layer electrically A first electrode connected to the first electrode, a second electrode electrically connected to the first material layer and the second material layer and spaced apart from the first electrode, and the first material layer, A substrate on which a unit structure is formed by the second material layer, and the interface between the first material layer and the second material layer is between the first material layer and the second material layer. When the electric polarization of the electric conduction layer is discontinuous, an electric conduction layer mainly responsible for electric conduction is generated, and the first electrode and the second electrode are electrically connected to the electric conduction layer when the electric conduction layer is generated. The connected state, the difference in electric polarization at the interface between the first material layer and the second material layer is Seebeck coefficient of the gas conduction layer is set in a relationship such as increased according to the increase of the carrier concentration of the electrically conductive layer, a unit structure of the first material layer and the second material layer, the first There is provided a thermoelectric conversion element formed over a plurality of layers so that an interface between the material layer and the second material layer and a surface of the substrate are perpendicular to each other.

According to another aspect of the present embodiment, the first material layer, the second material layer disposed in contact with the first material layer, the first material layer and the second material layer electrically A first electrode connected to the first electrode, a second electrode electrically connected to the first material layer and the second material layer and spaced apart from the first electrode, and the first material layer, A substrate on which a unit structure is formed by the second material layer, and the interface between the first material layer and the second material layer is between the first material layer and the second material layer. When the electric polarization of the electric conduction layer is discontinuous, an electric conduction layer mainly responsible for electric conduction is generated, and the first electrode and the second electrode are electrically connected to the electric conduction layer when the electric conduction layer is generated. The connected state, the difference in electric polarization at the interface between the first material layer and the second material layer is Gas dimensionless performance index of the conductive layer is set in a relationship such as increased according to the increase of the carrier concentration of the electrically conductive layer, a unit structure of the first material layer and the second material layer, the There is provided a thermoelectric conversion element formed over a plurality of layers so that an interface between the first material layer and the second material layer and a surface of the substrate are perpendicular to each other.

  According to another aspect of the present embodiment, a thermoelectric power generation device including the thermoelectric conversion element described above is provided.

  According to the other aspect of this Embodiment, a Peltier device provided with said thermoelectric conversion element is provided.

According to another aspect of this embodiment, a manufacturing method of the thermoelectric conversion element, comprising the steps of preparing the substrate for forming the second material layer and the first material layer, wherein the first forming a _{Al a Ga b in 1-a} -b N (0 ≦ a ≦ 1,0 ≦ b ≦ 1,0 ≦ a + b ≦ 1) layer on the substrate to form the material layer and the second material layer When the _{Al a Ga b in 1-a} -b N (0 ≦ a ≦ 1,0 ≦ b ≦ 1,0 ≦ a + b ≦ 1) in layer _{Al c Ga d in 1-c} -d N (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, 0 ≦ c + d ≦ 1) layers, and the Al _a Ga _b In ₁ -abN (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦) a + b ≦ 1) layer and a step of etching the Al _c Ga _d In _1-cd N (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, 0 ≦ c + d ≦ 1) layer. Way provided That.

According to another aspect of this embodiment, a manufacturing method of the thermoelectric conversion element, comprising the steps of preparing the substrate for forming the second material layer and the first material layer, said first material forming a _{Al a Ga b in 1-a} -b N (0 ≦ a ≦ 1,0 ≦ b ≦ 1,0 ≦ a + b ≦ 1) layer on the substrate forming the the layer second material layer the _{Al a Ga b in 1-a} -b N (0 ≦ a ≦ 1,0 ≦ b ≦ 1,0 ≦ a + b ≦ 1) on a layer _{Al c Ga d in 1-c} -d N (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, 0 ≦ c + d ≦ 1) layer, and the Al _a Ga _b In _1- abN (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b) ≦ 1) A step of forming a region in which an electrode is formed by opening a wall of the Al _c Ga _d In _1-cd N (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, 0 ≦ c + d ≦ 1) layer. Of thermoelectric conversion elements having Granulation method is provided.

  According to the present embodiment, the trade-off between Seebeck coefficient and carrier concentration, and the trade-off between Seebeck coefficient and electric conductivity, and a thermoelectric conversion element that can be stacked with high electric conductivity, and a method for manufacturing the thermoelectric conversion element, and this A thermoelectric generator and a Peltier device using a thermoelectric conversion element can be provided.

The typical cross-section of the thermoelectric conversion element which concerns on 1st Embodiment, and the energy band figure calculated in 2DEG vicinity. In the thermoelectric conversion element according to the first embodiment, a Hall effect measurement device configuration for evaluating sheet electron concentration n (cm ⁻² ) and electron mobility μ (cm ² V ⁻¹ s ⁻¹ ) FIG. In the thermoelectric conversion element according to the first embodiment, the measured sheet carrier concentration n (cm ⁻² ), the calculated 2DEG layer thickness t _2D , and the calculation for the sample in which the Al molar fraction X was changed The figure which shows the carrier density n (cm < ^-3 >) done. The figure which shows the relationship between the carrier mobility (micro | micron | mu) in the 2DEG layer, electrical conductivity (sigma), and carrier concentration n in the thermoelectric conversion element which concerns on 1st Embodiment. FIG. 3 is a schematic bird's-eye view structure diagram illustrating a measurement system for the Seebeck coefficient S by disposing the thermoelectric conversion element according to the first embodiment between a heat sink and a heater. The figure which shows the thermoelectric conversion characteristic about the sample D5 shown by FIG. 3 in the thermoelectric conversion element which concerns on 1st Embodiment. The parameter for calculating the absolute value | S | of the Seebeck coefficient S and the calculation result of the absolute value | S | in the thermoelectric conversion element according to the first embodiment. The figure which shows the relationship between Seebeck coefficient S and carrier concentration n in the thermoelectric conversion element which concerns on 1st Embodiment. The figure which shows the relationship between the dimensionless figure of merit ZT and carrier concentration n in the thermoelectric conversion element which concerns on 1st Embodiment. (a) The typical cross-section figure of the thermoelectric conversion element which concerns on 2nd Embodiment, (b) The typical cross-section structure figure of the thermoelectric conversion element which concerns on the modification of 2nd Embodiment. The typical cross-section figure of the thermoelectric conversion element which concerns on 3rd Embodiment. The typical cross-section figure of the thermoelectric conversion element which concerns on 4th Embodiment. The typical cross-section figure of the thermoelectric conversion element which concerns on 5th Embodiment. The typical cross-section figure of the thermoelectric conversion element which concerns on 6th Embodiment. The typical cross-section figure of the thermoelectric conversion element which concerns on 7th Embodiment. It is a manufacturing method of the thermoelectric conversion element which concerns on 7th Embodiment, Comprising: (a) The typical cross-section figure which shows the process of preparing a sapphire substrate, (b) The process of forming a GaN layer on a sapphire substrate is shown. FIG. 2 is a schematic cross-sectional structure diagram, (c) a schematic cross-sectional structure diagram illustrating a process of etching a GaN layer, and (d) a schematic cross-sectional structure diagram illustrating a process of forming an AlGaN layer on a sapphire substrate. (A) Explanatory drawing of the operation principle of the thermoelectric generator according to the basic technology, (b) Current-voltage characteristics of the thermoelectric generator at a temperature change ΔT. The typical block diagram of the thermoelectric power generating apparatus which concerns on basic technology (example provided with a heat sink in the low temperature side, and a heat exchanger in the high temperature side). The typical block diagram of the thermoelectric generator which concerns on basic technology (The example which has arrange | positioned the several thermoelectric generator in series). It is a thermoelectric power generating apparatus which concerns on 8th Embodiment, Comprising: (a) Typical top view, (b) Typical bird's-eye view block diagram. It is a thermoelectric power generation apparatus which concerns on 9th Embodiment, Comprising: (a) Typical top view, (b) Typical bird's-eye view block diagram. It is a thermoelectric power generation apparatus which concerns on 10th Embodiment, Comprising: (a) Typical top view, (b) Typical bird's-eye view block diagram.

  Next, the present embodiment will be described with reference to the drawings. In the following, the same reference numerals are assigned to the same blocks or elements to avoid duplication of explanation and simplify the explanation. It should be noted that the drawings are schematic and different from the actual ones. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  The embodiment described below exemplifies an apparatus and a method for embodying the technical idea, and does not specify the arrangement of each component as described below. This embodiment can be modified in various ways within the scope of the claims.

[First embodiment]
A schematic cross-sectional structure of the thermoelectric conversion element 10 according to the first embodiment and a calculated energy band diagram in the vicinity of the 2DEG layer are expressed as shown in FIG.

Further, in the thermoelectric conversion element 10 according to the first embodiment, for the Hall effect measurement for evaluating the sheet electron concentration n (cm ⁻² ) and the electron mobility μ (cm ² V ⁻¹ s ⁻¹ ). A schematic bird's-eye view structure of the device configuration is expressed as shown in FIG.

As shown in FIGS. 1 to 2, the thermoelectric conversion element 10 according to the first embodiment includes a first material layer 12, a second material layer 14 disposed in contact with the first material layer 12, and First electrodes 16 ₁ and 16 ₂ electrically connected to the first material layer 12 and the second material layer 14, and electrically connected to the first material layer 12 and the second material layer 14, and the first electrode 16 ₁ and 16 ₂ and second electrodes 18 ₁ and 18 ₂ formed apart from each other.

Here, at the interface between the first material layer 12 and the second material layer 14, the electric polarization mainly between the first material layer 12 and the second material layer 14 is caused by the discontinuity of the electric polarization between the first material layer 12 and the second material layer 14. When the conductive layer is generated, the first electrodes 16 ₁ and 16 ₂ and the second electrodes 18 ₁ and 18 ₂ are electrically connected to the electrical conductive layer when the electrical conductive layer is generated. The difference in electric polarization at the interface between the first material layer 12 and the second material layer 14 is set so that the Seebeck coefficient S of the electric conductive layer increases as the reduced Fermi energy ζ increases.

The thermoelectric conversion element 10 according to the first embodiment is capable of converting thermal energy associated with a temperature difference between the first electrodes 16 ₁ , 16 ₂ and the second electrodes 18 ₁ , 18 ₂ into electrical energy, It is possible to convert electric energy by applying a current between the first electrodes 16 ₁ and 16 ₂ and the second electrodes 18 ₁ and 18 ₂ into a temperature difference.

Here, the temperature difference between the first electrodes 16 ₁ and 16 ₂ and the second electrodes 18 ₁ and 18 ₂ is, for example, that the thermoelectric conversion element 10 is disposed between the heat sink 200 and the heater 300 as shown in FIG. Can be obtained by:

  Here, the second material layer 14 may include a semiconductor.

  The first material layer 12 may include a GaN layer, and the second material layer 14 may include an AlGaN layer.

The first material layer 12 includes Al _a Ga _b In ₁ -abN (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1), and the second material layer 14 includes the first material layer 14. Al _c Ga _d In _1-cd N (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, 0 ≦ c + d ≦ 1) having a composition different from that of the material layer 12 may be provided.

  The second material layer 14 may be formed of a material that does not contain N.

  The first material layer 12 may include a ferroelectric material.

  In addition, a substrate on which a unit structure formed by the first material layer 12 and the second material layer 14 is formed is provided. A plurality of layers may be laminated so that the interface between the two material layers 14 and the surface of the substrate are parallel to each other.

  In addition, a substrate on which a unit structure formed by the first material layer 12 and the second material layer 14 is formed is provided. It may be formed over a plurality of layers so that the interface between the two material layers 14 and the surface of the substrate are perpendicular to each other.

  In addition, in the direction perpendicular to the interface between the first material layer 12 and the second material layer 14, a layer that is not necessarily the same layer structure and mainly responsible for electrical conduction is sandwiched between the first material layer 12 and the second material layer 14. The unit structure may be repeatedly laminated.

  Further, the substrate on which the first material layer 12 and the second material layer 14 are formed may contain silicon.

  Moreover, the board | substrate which forms the 1st material layer 12 and the 2nd material layer 14 may contain sapphire.

The first electrodes 16 ₁ and 16 ₂ and the second electrodes 18 ₁ and 18 ₂ may be formed in contact with the electrically conductive layer.

The first electrodes 16 ₁ and 16 ₂ and the second electrodes 18 ₁ and 18 ₂ may be in ohmic contact with the electrically conductive layer.

The first electrodes 16 ₁ and 16 ₂ and the second electrodes 18 ₁ and 18 ₂ may be connected to the second material layer 14.

The first electrodes 16 ₁ and 16 ₂ and the second electrodes 18 ₁ and 18 ₂ may be made of the same material.

The thermoelectric conversion element 10 according to the first embodiment includes a first material layer 12, a second material layer 14 disposed in contact with the first material layer 12, the first material layer 12, and the second material layer 12. The first electrodes 16 ₁ , 16 ₂ electrically connected to the material layer 14 and the first electrodes 16 ₁ , 16 ₂ electrically connected to the first material layer 12 and the second material layer 14 are spaced apart from the first electrodes 16 ₁ , 16 _2. And the second electrode 18 ₁ , 18 ₂ formed at the interface, the electric polarization between the first material layer 12 and the second material layer 14 at the interface between the first material layer 12 and the second material layer 14. When the electric conduction layer is generated, the first electrode 16 ₁ , 16 ₂ and the second electrode 18 ₁ , 18 ₂ are formed in the electric conduction layer when the electric conduction layer is generated. The difference in electrical polarization at the interface between the first material layer 12 and the second material layer 14 is due to the electrical connection. Seebeck coefficient S of the conductive layer may be set in relation to increase with an increase in the carrier concentration n of the electrically conductive layer.

According to another aspect of the present embodiment, the first material layer 12, the second material layer 14 disposed in contact with the first material layer 12, the first material layer 12 and the second material layer 14, The first electrodes 16 ₁ and 16 ₂ that are electrically connected, and the first material layer 12 and the second material layer 14 are electrically connected and are spaced apart from the first electrodes 16 ₁ and 16 ₂ . The second electrodes 18 ₁ and 18 ₂ are provided, and the electric polarization between the first material layer 12 and the second material layer 14 is discontinuous at the interface between the first material layer 12 and the second material layer 14. As a result, an electric conduction layer mainly responsible for electric conduction is generated, and the first electrodes 16 ₁ and 16 ₂ and the second electrodes 18 ₁ and 18 ₂ are electrically connected to the electric conduction layer when the electric conduction layer is generated. The difference in electric polarization at the interface between the first material layer 12 and the second material layer 14 is the dimensionless property of the electric conduction layer. Index ZT may be set in relation to increase with an increase in the carrier concentration n of the electrically conductive layer.

  In the thermoelectric conversion element 10 according to the first embodiment, the electrical conductive layer mainly responsible for electrical conduction is a 2DEG layer, a two-dimensional hole gas (2DHG) layer, or a 2DEG layer and a 2DHG layer. You may have both.

In the thermoelectric conversion element 10 according to the first embodiment, the first electrodes 16 ₁ , 16 ₂ and the second electrodes 18 ₁ , 18 ₂ are electrodes of the same material configuration and are layers mainly responsible for electrical conduction. Is in ohmic contact.

  Further, in the thermoelectric conversion element 10 according to the first embodiment, the first material layer 12 and the second material layer 14 have different electric polarizations, and at the interface between the first material layer 12 and the second material layer 14. The electric polarization may be discontinuous.

Further, in the thermoelectric conversion element 10 according to the first embodiment, as shown in FIG. 1, the electric polarization in the second material layer 14 is the sum of the spontaneous polarization P _SP and the piezo polarization P _PE accompanying the piezo electric field. It is represented by (P _SP + P _PE ), and the electric polarization in the first material layer 12 is represented by spontaneous polarization P _SP and has an electric polarization discontinuity.

  Moreover, in the thermoelectric conversion element 10 which concerns on 1st Embodiment, the Seebeck coefficient S of the thermoelectric conversion element 10 may be provided with the performance which increases in response to the increase in the carrier concentration which the thermoelectric conversion element 10 hold | maintains. .

  Further, in the thermoelectric conversion element 10 according to the first embodiment, the Seebeck coefficient S of the thermoelectric conversion element 10 increases in response to an increase in the carrier concentration n of a layer responsible for electrical conduction such as a 2DEG layer or a 2DHG layer. It may have performance.

  Further, in the thermoelectric conversion element 10 according to the first embodiment, the first material layer 12 and the second material layer 14 may not be doped for the purpose of conductivity modulation of the 2DEG layer or the 2DHG layer. good.

  Further, in the thermoelectric conversion element 10 according to the first embodiment, a layer that is not necessarily the same layer configuration and mainly responsible for electrical conduction is provided in the direction perpendicular to the interface between the first material layer 12 and the second material layer 14. The unit structure sandwiched between the first material layer 12 and the second material layer 14 may be repeatedly laminated.

  In the thermoelectric conversion element 10 according to the first embodiment, as a method of overcoming the trade-off between the Seebeck coefficient S and the carrier concentration n and the trade-off between the Seebeck coefficient S and the electric conductivity σ, an unprecedented new concept is used. A two-dimensional electrically conductive layer is formed by polarization discontinuity in a polarization material that can be laminated. By increasing the amount of polarization of the polarization material, the carrier concentration of the two-dimensional electrically conductive layer can be increased, thereby causing the V-shaped recovery phenomenon of the Seebeck coefficient S. As a result, the trade-off between the Seebeck coefficient S and the electrical conductivity σ can be eliminated.

(Performance of thermoelectric conversion element)
The dimensionless figure of merit ZT of the thermoelectric conversion element is

ZT = S ² σ / κ · T (1)

It is represented by
Here, S represents the Seebeck coefficient, σ represents electrical conductivity, and κ represents thermal conductivity.

In addition, the Seebeck coefficient S in a commonly used n-type bulk material is

S = 8π ² κ _B ² T / 3 eh ² · m ^* · (π / 3n) ^2/3 (2)

Is represented. Where κ _B is the Boltzmann constant, T is the absolute temperature, e is the elementary charge of electrons, h is the Planck constant, m ^* is the effective mass of electrons, and n is the carrier concentration.

The electrical conductivity σ is

σ = neμ (3)

It is represented by Where μ is the electron mobility.

It is clear from the above formulas (1) and (2) that the Seebeck coefficient S and the electrical conductivity σ of the thermoelectric conversion element are in a trade-off relationship with the carrier concentration n. That is, it means that the Seebeck coefficient S decreases as the carrier concentration n increases. In addition, since the carrier concentration n also affects the thermal conductivity κ, it is generally said that the thermoelectric conversion element has the best performance at a carrier concentration of 10 ¹⁸ to 10 ¹⁹ (cm ⁻³ ). .

  In the thermoelectric conversion element according to the present embodiment, not only the Seebeck coefficient S increases at a relatively large carrier concentration n due to the electron confinement effect induced by the polarization effect, but also the Seebeck coefficient S and the carrier concentration n. The trade-off relationship is broken, and the V-shaped recovery characteristic can be obtained. Further, the increase in carriers is not induced by a gate bias, but is realized by a change in polarization effect.

  The V-shaped recovery characteristic between the Seebeck coefficient S and the carrier concentration n is a typical feature due to the electric polarization discontinuity configuration in the thermoelectric conversion element according to the first embodiment.

  In the thermoelectric conversion element according to the first embodiment, a polarization discontinuous structure is adopted, and as a result, a 2DEG structure (or 2DHG structure) appearing at the heterojunction interface is adopted as the polarization discontinuous structure. In addition, the polarization discontinuous configuration based on the 2DEG structure (or 2DHG structure) does not require impurity doping or inducement of a clear by gate bias.

  Such an intentionally undoped multilayer structure can not only reduce ionized impurity scattering, but also increase carrier mobility μ and increase electrical conductivity σ. Furthermore, except for the relatively very thin 2DEG layer (or 2DHG layer), most of the device region can be a heat conduction blocking region with a relatively low thermal conductivity κ.

  Furthermore, the thermoelectric conversion element according to the first embodiment can easily extend the unit structure of the 2DEG heterojunction (or 2DHG heterojunction), and can be stacked in a multilayer structure, with a relatively very thin 2DEG layer. Can compensate for the low electrical conduction characteristics.

  Therefore, the thermoelectric conversion element according to the present embodiment having the polarization discontinuous configuration can increase the dimensionless figure of merit ZT and at the same time achieve high electrical conductivity σ and low thermal conductivity κ performance.

  Therefore, the thermoelectric conversion element according to the first embodiment can have both excellent thermoelectric conversion performance and ease of manufacture.

(Material and forming method)
Al _X Ga _1-X N / GaN (0.2 <= X <= 0.4) is formed on the GaN template 11 formed on the sapphire substrate 100 by a low pressure metal organic vapor phase epitaxy (MOCVD: Metal Organic Vapor). (Phased Epitaxy). Here, the growth pressure is, for example, about 76 Torr, and the growth temperature is, for example, about 1333K.

Trimethylgallium (TMG) was used as a forming material for Ga, trimethylaluminum (TMAl) was used as a forming material for Al, and ammonia (NH ₃ ) was used as a forming material for N.

  After forming GaN growth nuclei on the (0001) plane sapphire substrate 100, the GaN template 11 is formed to a thickness of about 2 μm.

On the GaN template 11 is intentionally undoped _{Al X Ga 1-X N /} GaN (0.2 <= X <= 0.4) heterostructure is formed. Here, crystal growth is carried out in a hydrogen atmosphere with a fixed ammonia flow of 0.23 μmol / min.

The flow rate of TMG for GaN growth is 32.7 μmol / min. The Al mole fraction _{X of the} Al _x Ga _1-x N / GaN epitaxial growth layer reduces the TMG flow rate from 11.3 μmol / min to 5.78 μmol / min with a fixed TMAl flow of 1.62 μmol / min. This is applicable.

The thicknesses of the Al _x Ga _1-x N layer 14 and the GaN layer 12 are, for example, about 30 nm and about 1 μm, respectively.

  The Al mole fraction X was determined by reciprocal space mapping of X-ray scattering.

Further, for the measurement of the Hall effect of van der Pauw configuration, after the first electrodes 16 ₁ and 16 ₂ and the second electrodes 18 ₁ and 18 ₂ are formed on the Al _x Ga _1-x N layer 14 by electron beam evaporation, In order to make ohmic contact with the 2DEG layer at the Al _x Ga _1-x N / GaN heterojunction interface, for example, annealing is performed at about 823 K for about 10 minutes. The first electrodes 16 ₁ and 16 ₂ and the second electrodes 18 ₁ and 18 ₂ have an Al / Ti structure (a two-layer structure of Al formed on Ti and Ti). Here, the thickness of the Ti layer is about 20 nm, and the thickness of the Al layer is about 400 nm. As a result, as shown in FIG. 2, the circular first electrodes 16 ₁ , 16 ₂ and the second electrodes 18 ₁ , 18 ₂ arranged in a square pattern are formed on the Al _x Ga _1-x N layer 14. It is formed.

Next, as shown in FIG. 2, Al _x Ga _{1 is formed} into an approximately 3 mm × 3 mm shape by lithography and an inductively coupled plasma (ICP) etching method using a mixed gas of Cl ₂ and SiCl ₄ . _A mesa shape made of _-X N / GaN heterojunction is formed on the GaN template 11. The flow rates of Cl ₂ and SiCl ₄ are 15 sccm (standard cubic centimeter) and 5 sccm, respectively. A 13.56 MHz AC power of 50 W is supplied to the sample, and a power of 50 W is supplied to the ICP etching apparatus.

  All used in the experiment were also samples, and the etching depth was, for example, about 300 nm.

Hall effect measurement was performed at room temperature, and the sheet carrier concentration n (cm ⁻² ) and electron mobility μ (cm ² V ⁻¹ s ⁻¹ ) were measured.

(Electron mobility μ (cm ² V ⁻¹ s ⁻¹ ), sheet carrier concentration n (cm ⁻² ), carrier concentration n (cm ⁻³ ), electrical conductivity σ)
In the thermoelectric conversion element 10 according to the first embodiment, for the sample in which the Al molar fraction X is changed, the measured sheet carrier concentration n (cm ⁻² ), the calculated 2DEG layer thickness t _2D , The calculated carrier concentration n (cm ⁻³ ) is expressed as shown in FIG. Here, the calculated carrier concentration n (cm ⁻³ ) is equal to the value obtained by dividing the measured sheet carrier concentration n (cm ⁻² ) by the calculated 2DEG layer thickness t _2D .

In FIG. 3, samples with an Al molar fraction X = 0.2 correspond to A1-A5, samples with X = 0.3 correspond to B1-B3, and samples with X = 0.35 correspond to C1-C6. Correspondingly, the sample with X = 0.4 corresponds to D1 to D6, and the carrier concentration is determined by each measured sheet carrier concentration n (cm ⁻² ) and the calculated 2DEG layer thickness t _2D. n (cm ⁻³ ) is obtained.

In order to determine the thickness t _2D of the 2DEG layer, the energy of the Al _X Ga _1-X N / GaN system is obtained for a sample having a specific Al mole fraction X under the conditions of 300 K and an external bias voltage of 0 V. The band diagram was obtained by simulation. Here, TCAD (Technology Computer Aided Design) was applied as a simulator.

Next, as shown in the band structure of Figure 1, to determine the thickness t _2D of the 2DEG layer by a band region width Fermi level E _F is present above the conduction band E _C in the GaN layer 12.

The sample used for the simulation includes an Al _x Ga _1-x N layer 14 having a thickness of 30 nm and a GaN layer 12 having a thickness of 1 μm, and the carrier concentration of each layer of the Al _x Ga _1-x N layer 14 and the GaN layer 12. n was set to 1.0 × 10 ¹⁶ (cm ⁻³ ). Also, in the TCAD simulation, the electron trap level is not considered for the sake of simplicity. This is because the simplest case should be considered and the physical phenomenon of defects in the Al _x Ga _1-x N / GaN system is still complicated.

The electrical conductivity σ (Scm ⁻¹ ) was determined using the formula (2).

These calculated 2DEG layer thicknesses t _2D are represented in a continuous range from 5.7 nm for Al _0.2 Ga _0.8 N to 7.0 nm for Al _0.4 Ga _0.6 N, as shown in FIG. These values are used in calculating the carrier concentration n.

(Relationship between carrier mobility μ, electrical conductivity σ, and carrier concentration n)
In the thermoelectric conversion element 10 according to the first embodiment, carrier mobility μ (cm ² V ⁻¹ s ⁻¹ ) and electric conductivity σ (Scm ⁻¹ ) in the 2DEG layer, and carrier concentration n (cm ^−3). ) Is expressed as shown in FIG.

(Measurement of Seebeck coefficient S)
After the Hall effect measurement, the in-plane Seebeck coefficient S of the thermoelectric conversion element 10 according to the first embodiment was measured at room temperature for the sample shown in FIG.

  A schematic bird's-eye view structure in which the thermoelectric conversion element 10 according to the first embodiment is arranged between the heat sink 200 and the heater 300 and the measurement system of the Seebeck coefficient S is expressed as shown in FIG.

  As shown in FIG. 5, the thermoelectric conversion element 10 according to the first embodiment is disposed between the heat sink 200 and the heater 300 so as to generate a specific temperature difference.

  The thermoelectric characteristics of the thermoelectric conversion element 10 according to the first embodiment were measured using the voltage probes 22A and 22B and the type K thermocouples 24A and 24B having a diameter of about 150 μm.

  The sample temperatures of the heat sink 200 side and the heater 300 side were measured using type K thermocouples 24A and 24B.

  The temperature of the heater 300 can be controlled by a DC voltage source. The output voltage of the DC voltage source can be increased stepwise from 0V to 30V in 5V steps.

  The low temperature side of the thermoelectric conversion element 10 according to the first embodiment may be naturally air-cooled.

  The measurement of the Seebeck coefficient S was carried out after a sufficient time interval for temperature stabilization.

(Thermoelectric conversion characteristics for sample D5)
In the thermoelectric conversion element 10 according to the first embodiment, the thermoelectric conversion characteristics of the sample D5 shown in FIG. 3 are expressed as shown in FIG. FIG. 6 shows the measurement result of the Seebeck coefficient S. In FIG. 6, “Applied voltage (current)” indicates the output voltage (current) of the DC voltage source. T _high (K) and T _low (K) indicate measured temperatures on the heater 300 side and the heat sink 200 side, respectively.

ΔT (K) is equal to T _high (K) −T _low (K). ΔV (μV) indicates a difference voltage between the measured voltages detected by the type K thermocouples 24A and 24B.

The Seebeck coefficient S (μV · K ⁻¹ ) is equal to ΔV / ΔT.

(Theoretical calculation of Seebeck coefficient S)
In the thermoelectric conversion element 10 according to the first embodiment, the parameters for calculating the absolute value | S | of the Seebeck coefficient S and the calculation results of the absolute value | S | are expressed as shown in FIG.

  If the energy level of all electrons in the energy gap (forbidden band width) of GaN can be considered, the carrier concentration n can be uniquely determined by the specific Al mole fraction X. However, compared with the carrier concentration n obtained by the specific Al mole fraction X shown in FIG. 3, the value of the carrier concentration n obtained experimentally includes a non-negligible displacement. This means that the experiment includes various factors such as dislocations and surface states. Therefore, it is impractical to calculate the carrier concentration directly.

  Therefore, in FIG. 7 in which the relationship between the absolute value | S | of the Seebeck coefficient S and the carrier concentration n is obtained, for a specific Al mole fraction X (= 0.2, 0.3, 0.4), Using the averaged value (n bar) of the experimental carrier concentration n shown in FIG. 3, for a specific Al mole fraction X (= 0.25 and 0.35), the experimental It was calculated by linear approximation of the averaged value (n bar) of the carrier concentration n.

(Relationship between Seebeck coefficient S and carrier concentration n)
In the thermoelectric conversion element 10 according to the first embodiment, the relationship between the Seebeck coefficient S and the carrier concentration n is expressed as shown in FIG. FIG. 8 shows the relationship between the absolute value | S | of the Seebeck coefficient S and the carrier concentration n. Here, in FIG. 8, | S | _2DEG represents the absolute value of the Seebeck coefficient S for the AlGaN / GaN-based sample used in the experiment. Further, | S | _film-GaN represents the absolute value of Seebeck coefficient S of bulk GaN published in Non-Patent Document 10 as a comparative example.

As shown in FIG. 8, the absolute value | S | _2DEG of the Seebeck coefficient S is substantially larger than the value of | S | _film-GaN in the range of the carrier concentration n shown in FIG. The absolute value of the Seebeck coefficient S | S | increasing tendency of _{the 2DEG,} level density of the physical theory Fermi level E _F electrons in the vicinity (DOS: density of states) is described as increased by the quantum size effect of the energy differential value of The That is, S∝ [dDOS (E) / dE] _E-EF is established.

The quantum size effect of the thin film GaN is assumed to occur at a thickness of about 20 nm to about 30 nm or less. In the sample of the thermoelectric conversion element 10 according to the first embodiment applied to the experiment, the thickness t _2D Is well within this range.

In the thermoelectric conversion element 10 according to the first embodiment, as shown in FIG. 8, the Seebeck coefficient S is such that the carrier concentration n is greater than about 3.5 × 10 ¹⁹ cm ⁻³ and the carrier concentration n Despite the increase, the V-shaped recovery characteristic of increasing from 170 (μV · K ⁻¹ ) to 300 (μV · K ⁻¹ ) is shown.

In the thermoelectric conversion element 10 according to the first embodiment, the 2DEG confined in the triangular potential as shown in FIG. 1 increases the carrier concentration n of the absolute value | S | _2DEG of the Seebeck coefficient S. There is an accompanying increasing trend.

(Theoretical analysis)
The Seebeck coefficient S _i of the i-th subband of electrons confined in the quantum well (QW) is

S _i = κ _B / e · [2F _j (ζ _i ^* ) / F ₀ (ζ _i ^* ) − ζ _i ^* ] (4)

It is represented by Here, F _j is an indefinite integral including a Fermi-Dirac distribution function given by the following equation (5).

F _j (ζ _j ^* ) = ∫ ₀ ^∞ x ^j dX / [exp (x−ζ _j ^* ) + 1] (5)

Here, ζ _i ^* = (E _F −E _i ) / k _B T, and ζ _i ^* represents the reduced Fermi energy with respect to the energy E _i of the quantized i-th subband.

Here, it is assumed that all electrons exist at the energy level E ₀ (minimum energy of the quantization subband), and i = 0 is set. It is also assumed that the theoretical preconditions for obtaining equations (4) and (5) are applicable for calculating the theoretical Seebeck coefficient (Calculated | S | _2DEG ). Here, the second assumption includes the assumption of simplification of the electron scattering mechanism. Polar optical (PO) phonon scattering and acoustic (AC) acoustic phonon scattering are the main electron scattering mechanisms in GaN.

The inverse relaxation time 1 / τ of PO phonon scattering is expressed as a function of perturbation intensity instead of electron energy. On the other hand, x ^j appearing in the equation (5) is expressed as a j-th power term of a series developed as a function of the energy of the electron having the inverse relaxation time 1 / τ. This means that equation (5) does not deal with the effects of PO phonons, and the Seebeck coefficient S theoretical calculation only deals with AC phonon scattering.

The reduced Fermi energy ζ _i ^* in the equation (4) is a factor related to the carrier concentration n and is not affected by the scattering mechanism. “E _F -E _i ” of each Al _X Ga _1-X N / GaN sample is calculated by TCAD simulation. The calculated Seebeck coefficient: Calculated | S | _2DEG is represented by a broken line in a circle plot in FIG. On the horizontal axis in FIG. 8, the averaged carrier concentration n bar is used as the carrier concentration n.

In FIG. 8, the relationship between the calculated Seebeck coefficient: Calculated | S | _2DEG and the carrier concentration n can be qualitatively reproduced for a carrier concentration n of about 2 × 10 ¹⁹ cm ⁻³ or more. Here, the value of the carrier concentration n of about 2 × 10 ¹⁹ cm ⁻³ corresponds to the averaged carrier concentration bar n of the Al _0.2 Ga _0.8 N / GaN sample.

The function F _j (ζ _i ^* ) in equation (5) can be approximated by exp (ζ _i ^* ) using an asymptotic extension to the Fermi-Dirac integral in a non-degenerate semiconductor, “F ₁ (ζ ₁ ^* ) / F ₀ (ζ ₁ ^* )” can be fixed to 1. Further, “E _F −E ₀ ” can be calculated by TCAD simulation under the same conditions as the above-described conditions for calculating t _2D . As a result, the absolute value | S | of the Seebeck coefficient S can be calculated using the equation (4).

  In general, the performance of thermoelectric conversion elements is limited by material selection. That is, the thermoelectric properties of the bulk material are theoretically determined by a factor depending on the material, that is, the electric conductivity σ and the Seebeck coefficient S. As shown in the equations (2) and (3), when the carrier concentration n is increased, there is a common trade-off relationship depending on the material that the Seebeck coefficient S decreases although the electrical conductivity σ increases.

  However, in the thermoelectric conversion element 10 according to the first embodiment, as shown by the ● plot in FIG. 8, in the region where the carrier concentration n of the 2DEG layer at the AlGaN / GaN heterostructure interface is relatively high, the carrier concentration When n is increased, the electrical conductivity σ increases, but the characteristic that the Seebeck coefficient S decreases disappears, and a characteristic of V-shaped recovery is obtained.

In the thermoelectric conversion element 10 according to the first embodiment, as shown in FIG. 8, the Seebeck coefficient S is a carrier concentration n when the carrier concentration n is about 3.5 × 10 ¹⁹ cm ⁻³ or more. When it increases, the characteristic that the Seebeck coefficient S decreases disappears, and a characteristic of V-shaped recovery is obtained.

(Relationship between dimensionless figure of merit ZT and carrier concentration n)
In the thermoelectric conversion element 10 according to the first embodiment, the relationship between the dimensionless figure of merit ZT at 300K and the carrier concentration n is expressed as shown in FIG. Here, it is assumed that the thermal conductivity κ of GaN is maintained at 120 W · m ⁻¹ · K ⁻¹ . In the thermoelectric conversion element 10 according to the first embodiment, the AlGaN / GaN heterostructure is intentionally undoped, and most regions of the device excluding the 2DEG layer having a thickness of 10 nm or less are substantially free from electrons. This is because it is equivalent to a bulk material. The 2DEG layer thickness t _2D can be obtained by calculation.

As shown in FIG. 9, the highest dimensionless figure of merit ZT at 300K is obtained as 0.141 at the carrier concentration n = 6.5 × 10 ¹⁹ cm ⁻³ . The dimensionless figure of merit ZT of bulk GaN is 0.002. Therefore, in the thermoelectric conversion element 10 according to the first embodiment, the dimensionless figure of merit ZT at 300K has an improvement effect of 70 times.

(V-shaped recovery characteristics)
If it is described in terms of the amount of polarization and the carrier concentration n, it will be a value only for the GaN-based material, so the theoretical characteristics will be described in consideration of application in other material systems.

In the 2DEG layer between materials having a polarization difference, the quantum effect occurs, so that the Fermi energy becomes higher than the ground level of the quantum level in the energy band, and represents the Seebeck coefficient S _i (6) ) In which the reduced Fermi energy ζ _i ^* is calculated from the Fermi-Dirac distribution function (A + 5/2) F _{A +} 3/2 (ζ _i ^* ) / (A + 3/2) F _{A + 1/2} ( ζ _i ^* ), that is, (A + 5/2) F _{A +} 3/2 (ζ _i ^* ) / (A + 3/2) F _{A + 1/2} (ζ _i ^* ) becomes a negative value. Then V-shape recovery of the Seebeck coefficient occurs. A is a value applied to the expression τ (E / k _B T) = τ ₀ (E / k _B T) ^A related to the relaxation time of carrier scattering.

_{S i = k B / e ·} [(A + 5/2) F A + 3/2 (ζ i *) / (A + 3/2) F A + 1/2 (ζ i *) -ζ i *]
(6)

Here, the relationship between the equations (4) and (5) is established similarly.

In the case of the 2DEG layer, ζ _i ^* = (E _F −E _i ) / k _B T. In the case of the 2DHG layer, ζ _i ^* = − (E _F −E _i ) / k _B T. It becomes. Since e in equation (6) is also a hole, it is a positive value.

The quantum effect is said to occur at about twice the exciton Bohr radius determined by the effective mass. In the case of GaN, it is said that a quantum effect occurs at 20 nm to 30 nm or less. For example, in 2DEG in the AlGaN / GaN system, the Al molar fraction X needs to be 0.2 or more and the carrier concentration needs to be 2 × 10 ¹⁹ cm ⁻³ or more.

  The thermoelectric conversion element 10 according to the first embodiment can be easily formed by a film laminated structure, and a superlattice structure or a phonon crystal having a low thermal conductivity κ can be applied.

  Therefore, according to the first embodiment, the electrical polarization discontinuity structure showing the V-shaped recovery performance and the superlattice structure or phonon crystal having a low thermal conductivity κ are fused to obtain a relatively high dimensionless performance. A thermoelectric conversion element having an index ZT can be provided.

  According to the first embodiment, the trade-off between the Seebeck coefficient and the carrier concentration and the trade-off between the Seebeck coefficient and the electric conductivity are improved, and a thermoelectric conversion element that can be stacked with a high electric conductivity is provided. it can.

  According to the first embodiment, the trade-off in which the Seebeck coefficient S decreases as the carrier concentration n increases is not only solved by using the V-shaped recovery phenomenon of the Seebeck coefficient S, but also can be stacked. By forming a polarization discontinuity in the polarization material and laminating, the trade-off between the Seebeck coefficient S and the electrical conductivity σ is solved, and a thermoelectric conversion element that achieves a high dimensionless figure of merit ZT is provided. it can.

  According to the first embodiment, when a laminated structure is used, a thermoelectric conversion element that further improves electric conductivity σ by forming both n-type and p-type in one element Can be provided.

[Second Embodiment]
(Structure with one electrically conductive layer)
The schematic cross-sectional structure of the thermoelectric conversion element 10 according to the second embodiment is expressed as shown in FIG. 10A, and the schematic cross-section of the thermoelectric conversion element 10 according to the modification of the second embodiment. The structure is represented as shown in FIG.

  As shown in FIG. 10A, the thermoelectric conversion element 10 according to the second embodiment includes a substrate 100, a GaN layer 12 disposed on the substrate 100, a GaN layer 12, and a GaN layer. 12, an AlGaN layer 14 having polarization discontinuity, a 2DEG layer formed at the interface between the GaN layer 12 and the AlGaN layer 14, and a first electrode 16 and a second electrode 18 that are in contact with the 2DEG layer from the side.

  Here, the substrate 100 may be a sapphire substrate.

  The GaN layer 12 surface on which the AlGaN layer 14 is formed may be an m-plane.

  As shown in FIG. 10B, the thermoelectric conversion element 10 according to the modification of the second embodiment is disposed on the substrate 100, the GaN layer 12 disposed on the substrate 100, and the GaN layer 12. The GaN layer 12 and the AlGaN layer 14 where polarization discontinuity occurs, the 2DEG layer formed at the interface between the GaN layer 12 and the AlGaN layer 14, and the first electrode 16 and the second electrode 18 disposed on the AlGaN layer 14 With. Similarly, the substrate 100 may be a sapphire substrate. The GaN layer 12 surface on which the AlGaN layer 14 is formed may be an m-plane.

  As an example, a structure composed of an AlGaN layer 14 / GaN layer 12 is fabricated on a sapphire substrate 100, a first electrode 16 and a second electrode 18 such as Ti / Al / Ni / Au are formed, and ohmic is obtained by sintering. Form.

  If necessary, device isolation can be performed thereafter.

  Instead of the AlGaN layer 14, an AlN layer, an AlInN layer, or the like may be used.

Further, a ferroelectric material such as PZT, BiFeO _3, or BaTiO ₃ may be used as the polarization material. If the polarization discontinuity occurs, or a combination of different materials compositions as _{Al x Ga 1-x N /} Al y Ga 1-y N (x ≠ y).

  In the second embodiment, similarly to the first embodiment, the trade-off between the Seebeck coefficient and the carrier concentration, and the trade-off between the Seebeck coefficient and the electric conductivity can be improved, and stacking can be performed with high electric conductivity. A thermoelectric conversion element can be provided.

  Also in the second embodiment, as in the first embodiment, the trade-off in which the Seebeck coefficient S decreases as the carrier concentration n increases is solved by using the V-shaped recovery phenomenon of the Seebeck coefficient S. In addition to forming and stacking polarization discontinuities in polarization materials that can be laminated, the trade-off between the Seebeck coefficient S and the electrical conductivity σ is solved, and a high dimensionless figure of merit ZT is achieved. A thermoelectric conversion element can be provided.

  Also in the second embodiment, as in the first embodiment, when a stacked structure is used, by forming both n-type / p-type in one element, further electrical conductivity σ A thermoelectric conversion element that can be improved can be provided.

[Third embodiment]
(Structure with one electrically conductive layer with continuous polarization material)
A schematic cross-sectional structure of the thermoelectric conversion element 10 according to the third embodiment is expressed as shown in FIG.

  As shown in FIG. 11, the thermoelectric conversion element 10 according to the third embodiment includes a silicon substrate 8, an AlN layer 13 disposed on the silicon substrate 8, and an interface between the silicon substrate 8 and the AlN layer 13. A 2DEG layer to be formed and an AlGaN layer 14 disposed on the AlN layer 13 are provided. Here, although not shown, the first electrode 16 and the second electrode 18 that are in contact with the 2DEG layer from the side surface may be provided. Alternatively, the first electrode 16 and the second electrode 8 disposed on the AlGaN layer 14 may be provided.

  As an example, in a structure in which a polarization material such as the AlGaN layer 14 / GaN layer 12 is continuously formed on the silicon substrate 8, a layer mainly responsible for electrical conduction cannot be formed at the AlGaN layer 14 / GaN layer 12 interface. A 2DEG layer is formed at the AlN layer 13 / Si interface.

  Although not shown, the first electrode 16 and the second electrode 18 that are in contact with the 2DEG layer from the side surface may be provided as in the first embodiment (FIG. 10A). .

  Moreover, you may provide the 1st electrode 16 and the 2nd electrode 18 arrange | positioned on the AlGaN layer 14 similarly to the modification (FIG.10 (b)) of 1st Embodiment.

  As an example, a structure composed of an AlGaN layer 14 / AlN layer 13 is formed on a silicon substrate 8, a first electrode 16 and a second electrode 18 such as Ti / Al / Ni / Au are formed, and ohmic is obtained by sintering. Form.

  If necessary, device isolation can be performed thereafter.

  An AlInN layer or the like may be used instead of the AlGaN layer 14.

Further, a ferroelectric material such as PZT, BiFeO _3, or BaTiO ₃ may be used as the polarization material. If that is the polarization discontinuity occurs, or a combination of different materials compositions as _{Al x Ga 1-x N /} Al y Ga 1-y N (x ≠ y).

  In the third embodiment, similarly to the first embodiment, the trade-off between the Seebeck coefficient and the carrier concentration, and the trade-off between the Seebeck coefficient and the electric conductivity can be improved, and stacking can be performed with high electric conductivity. A thermoelectric conversion element can be provided.

  In the third embodiment, as in the first embodiment, the trade-off in which the Seebeck coefficient S decreases as the carrier concentration n increases is solved by using the V-shaped recovery phenomenon of the Seebeck coefficient S. In addition to forming and stacking polarization discontinuities in polarization materials that can be laminated, the trade-off between the Seebeck coefficient S and the electrical conductivity σ is solved, and a high dimensionless figure of merit ZT is achieved. A thermoelectric conversion element can be provided.

  Also in the third embodiment, as in the first embodiment, when a stacked structure is used, by forming both n-type / p-type in one element, further electrical conductivity σ A thermoelectric conversion element that can be improved can be provided.

[Fourth embodiment]
(Laminated structure with two or more electrically conductive layers)
A schematic cross-sectional structure of the thermoelectric conversion element 10 according to the fourth embodiment is expressed as shown in FIG.

  In the thermoelectric conversion element 10 according to the fourth embodiment, as shown in FIG. 12, a pair of a GaN layer and an AlGaN layer is multilayered.

Thermoelectric conversion element 10 according to the fourth embodiment, as shown in FIG. 12, a GaN layer 12 _1, and the AlGaN layer 14 ₁ disposed on the GaN layer 12 ₁ is disposed on the AlGaN layer 14 ₁ that the GaN layer 12 _2, the AlGaN layer 14 ₂ disposed on the GaN layer 12 _2, the GaN layer 12 ₃ is disposed on the AlGaN layer 14 _2, AlGaN layer 14 ₃ is disposed on the GaN layer 12 ₃ When provided with a GaN layer 12 ₄ disposed on the AlGaN layer 14 _3, and an AlGaN layer 14 ₄ disposed on the GaN layer 12 _4.

Here, 2DEG layer is formed at the interface between the GaN layer 12 ₁ · AlGaN layer 14 _1, AlGaN layer 14 ₁ and the two-dimensional hole gas at the interface between the GaN layer _{12 2 (2DHG: Two Dimensional Hole} Gas) layer It is formed.

Similarly, a 2DEG layer is formed at the interface between the GaN layer 12 ₂ and the AlGaN layer 14 ₂ , the interface between the GaN layer 12 ₃ and the AlGaN layer 14 _3, and the interface between the GaN layer 12 ₄ and the AlGaN layer 14 ₄ .

Similarly, a 2DHG layer is formed at the interface between the AlGaN layer 14 ₂ and the GaN layer 12 ₃ and at the interface between the AlGaN layer 14 ₃ and the GaN layer 12 ₄ . Here, illustration has been omitted, GaN layer 12 ₁ is formed on a substrate such as a sapphire substrate.

  Although not shown in the figure, the first electrode 16E and the second electrode 18E that are in contact with the 2DEG layer from the side surface may be provided as in the first embodiment (FIG. 10A). . Moreover, you may provide the 1st electrode 16H and the 2nd electrode 18H which contact a 2DHG layer from a side surface.

  As an example, by laminating films such that AlGaN / GaN / AlGaN / GaN / AlGaN / GaN / AlGaN / GaN /... GaN / substrate causes polarization discontinuity, a 2DEG layer at each AlGaN / GaN interface, or By forming the 2DHG layer or both, the electrical conductivity σ can be increased.

  In the case of a laminated structure, since both a 2DEG layer and a 2DHG layer can be formed, both p-type and n-type thermoelectric conversion elements can be formed with one element.

  Since it is important that polarization discontinuity occurs, it is possible to form a thermoelectric conversion element having a laminated structure of AlInN / GaN or a laminated structure such as AlGaN / GaAs / Si / AlGaN.

  Moreover, a thermoelectric conversion element provided with the laminated structure which combined them like AlGaN / GaN / AlInN / GaN /.../ board | substrate can also be formed.

  In addition, depending on the material used, a laminated structure can also be formed by spin coating or sol-gel method.

  Also in the fourth embodiment, the trade-off between Seebeck coefficient and carrier concentration and the trade-off between Seebeck coefficient and electric conductivity can be improved, and a thermoelectric conversion element that can be stacked with high electric conductivity can be provided. .

  Also in the fourth embodiment, the trade-off in which the Seebeck coefficient S decreases as the carrier concentration n increases is not only solved by using the V-shaped recovery phenomenon of the Seebeck coefficient S, but can also be stacked. By forming a polarization discontinuity in a polarization material and laminating it, it is possible to provide a thermoelectric conversion element that solves the trade-off between the Seebeck coefficient S and the electrical conductivity σ and realizes a high dimensionless figure of merit ZT. .

  Also in the fourth embodiment, when a laminated structure is used, a thermoelectric conversion element that further improves electric conductivity σ is provided by forming both n-type and p-type in one element. Can do.

[Fifth embodiment]
A schematic cross-sectional structure of a thermoelectric conversion element 10 according to the fifth embodiment is expressed as shown in FIG.

Thermoelectric conversion element 10 according to the fifth embodiment, as shown in FIG. 13, a GaN layer 12 _1, and the AlGaN layer 14 ₁ disposed on the GaN layer 12 ₁ is disposed on the AlGaN layer 14 ₁ that the GaN layer 12 _2, the AlGaN layer 14 ₂ disposed on the GaN layer 12 _2, the GaN layer 12 ₃ is disposed on the AlGaN layer 14 _2, AlGaN layer 14 ₃ is disposed on the GaN layer 12 ₃ When provided with a GaN layer 12 ₄ disposed on the AlGaN layer 14 _3, and an AlGaN layer 14 ₄ disposed on the GaN layer 12 _4.

Here, a 2DEG layer is formed at the interface between the GaN layer 12 ₁ and the AlGaN layer 14 ₁ . Similarly, a 2DEG layer is formed at the interface between the GaN layer 12 ₂ and the AlGaN layer 14 ₂ , the interface between the GaN layer 12 ₃ and the AlGaN layer 14 _3, and the interface between the GaN layer 12 ₄ and the AlGaN layer 14 ₄ .

  Although not shown, the first electrode 16 and the second electrode 18 that are in contact with the 2DEG layer from the side surface may be provided as in the first embodiment (FIG. 10A). .

On the other hand, no 2DHG layer is formed at the interface between the AlGaN layer 14 ₂ and the GaN layer 12 ₃ and at the interface between the AlGaN layer 14 ₃ and the GaN layer 12 ₄ . Here, illustration has been omitted, GaN layer 12 ₁ is formed on a substrate such as a sapphire substrate.

  Also in the fifth embodiment, the trade-off between Seebeck coefficient and carrier concentration, and the trade-off between Seebeck coefficient and electric conductivity can be improved, and a thermoelectric conversion element that can be stacked with high electric conductivity can be provided. .

  Also in the fifth embodiment, the trade-off in which the Seebeck coefficient S decreases as the carrier concentration n increases is not only solved by using the V-shaped recovery phenomenon of the Seebeck coefficient S, but can also be stacked. By forming a polarization discontinuity in a certain polarization material and laminating it, it is possible to provide a thermoelectric conversion element that solves the trade-off between the Seebeck coefficient S and the electrical conductivity σ and realizes a high dimensionless figure of merit ZT. .

  Also in the fifth embodiment, when a laminated structure is used, a thermoelectric conversion element that further improves the electrical conductivity σ is provided by forming both n-type and p-type in one element. Can do.

[Sixth embodiment]
A schematic cross-sectional structure of the thermoelectric conversion element 10 according to the sixth embodiment is expressed as shown in FIG.

As shown in FIG. 14, the thermoelectric conversion element 10 according to the sixth embodiment includes a first polarization material P1 layer 20 ₁ and a second material B layer 20B disposed on the first polarization material P1 layer 20 _1. When the third and the material a layers 20A, and the second polarization material P2 layer 20 ₂ that are disposed on the third material a layer 20A, the first polarization material P1 layer disposed on the second material B layer 20B layer 20B comprising 20 ₁ and the 2DHG layer formed at the interface between the second material B layers 20B, and a third material a layer 20A and the 2DEG layer formed at the interface between the second polarization material P2 layer 20 _2.

The first polarization material P1 layer 20 ₁ and the second polarization material P2 layer 20 ₂ may use a ferroelectric material such as PZT, BiFeO ₃ or BaTiO ₃ . Further, if the polarization discontinuity occurs, or a combination of different materials compositions as _{Al x Ga 1-x N /} Al y Ga 1-y N (x ≠ y).

  The second material B layer 20B and the third material A layer 20A may be AlGaN layers or GaN layers.

The first polarization material P1 layer 20 _1, the second material B layer 20B is, if the polarization discontinuity occurs, as _{Al x Ga 1-x N /} Al y Ga 1-y N (x ≠ y) Also, a combination of materials having different compositions may be used.

Similarly, the third material A layer 20A · second polarization material P2 layer 20 _2, if the polarization discontinuity _{occurs, Al x Ga 1-x N} / Al y Ga 1-y N in (x ≠ y) Thus, a combination of materials having different compositions may be used.

  In addition, although illustration is abbreviate | omitted, you may provide the 1st electrode 16E and the 2nd electrode 18E which contact a 2DEG layer from a side surface similarly to 1st Embodiment (Fig.10 (a)). Moreover, you may provide the 1st electrode 16H and the 2nd electrode 18H which contact 2DHG layer from a side surface.

  Also in the sixth embodiment, the trade-off between Seebeck coefficient and carrier concentration and the trade-off between Seebeck coefficient and electrical conductivity can be improved, and a thermoelectric conversion element that can be stacked with high electrical conductivity can be provided. .

  Also in the sixth embodiment, the trade-off in which the Seebeck coefficient S decreases as the carrier concentration n increases is not only solved by using the V-shaped recovery phenomenon of the Seebeck coefficient S, but can also be stacked. By forming a polarization discontinuity in a certain polarization material and laminating it, it is possible to provide a thermoelectric conversion element that solves the trade-off between the Seebeck coefficient S and the electrical conductivity σ and realizes a high dimensionless figure of merit ZT. .

  Also in the sixth embodiment, when a laminated structure is used, a thermoelectric conversion element that further improves the electrical conductivity σ is provided by forming both n-type and p-type in one element. Can do.

[Seventh embodiment]
(Horizontal laminated structure)
The thermoelectric conversion elements according to the first to sixth embodiments mainly have a structure in which they are stacked on the substrate in a direction perpendicular to the substrate. However, the structure is not necessarily limited to a structure in which the substrate is stacked in the vertical direction.

  A schematic cross-sectional structure of the thermoelectric conversion element according to the seventh embodiment is expressed as shown in FIG.

  As shown in FIG. 15, the thermoelectric conversion element according to the seventh embodiment is disposed on the substrate 100, the GaN layer 12 patterned on the substrate 100, and the substrate 100 between the GaN layers 12. It comprises a layer 12 and a material layer (14) where polarization discontinuities occur.

  Here, the substrate 100 may be a sapphire substrate.

  Further, the material layer (14) in which polarization discontinuity occurs with the GaN layer 12 may be the AlGaN layer 14. In this case, a 2DEG layer may be formed at the interface between the GaN layer 12 and the AlGaN layer 14.

  The GaN layer 12 surface on which the AlGaN layer 14 is formed may be an m-plane.

(Method for manufacturing thermoelectric conversion element)
In the method for manufacturing a thermoelectric conversion element according to the seventh embodiment, a schematic cross-sectional structure showing a step of preparing the sapphire substrate 100 is expressed as shown in FIG. A schematic cross-sectional structure showing the process of forming the GaN layer 12 is represented as shown in FIG. 16B, and a schematic cross-sectional structure showing the process of etching the GaN layer 12 is shown in FIG. 16C. A schematic cross-sectional structure showing the step of forming the AlGaN layer 14 on the sapphire substrate sandwiched between the GaN layers 12 is expressed as shown in FIG.

The manufacturing method of the thermoelectric conversion element according to the seventh embodiment includes a step of preparing the substrate 100 on which the first material layer 12 and the second material layer 14 are formed, and the first material layer 12 and the second material layer 14. A step of forming an Al _a Ga _b In _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1) layer on the substrate 100 to be formed; and Al _a Ga _b In ₁₋ Al _c Ga _d In _1-cd N (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, on the _ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1) layer, 0 ≦ c + d ≦ 1) layer formation, Al _a Ga _b In ₁ -abN (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1) layer and Al _c Ga _d In _And a step of etching the 1-cdN (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, 0 ≦ c + d ≦ 1) layer.

Moreover, the manufacturing method of the thermoelectric conversion element which concerns on 7th Embodiment prepares the board | substrate 100 which forms the 1st material layer 12 and the 2nd material layer 14, and the 1st material layer 12 and the 2nd material layer Forming an Al _a Ga _b In _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1) layer on the substrate 100 on which the layer 14 is formed, and Al _a Ga _b In Al _c Ga _d In _1-cd N (0 ≦ c ≦ 1, 0 ≦ d ≦) on the _1-a-b N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1) layer 1, 0 ≦ c + d ≦ 1) layer formation, Al _a Ga _b In _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1) layer and Al _c Ga _{and d} In _1- cdN (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, 0 ≦ c + d ≦ 1), and a step of forming a region for forming an electrode by opening the wall.

  Hereinafter, with reference to FIG. 16A to FIG. 16D, a method for manufacturing a thermoelectric conversion element according to the seventh embodiment will be described.

  (A) First, as shown in FIG. 16A, a sapphire substrate 100 is prepared.

  (B) Next, as shown in FIG. 16B, a GaN layer 12 is formed on the sapphire substrate 100.

  (C) Next, a large number of, for example, line and space patterns are formed by lithography.

(D) Next, as shown in FIG. 16C, the GaN layer is etched using a resist, SiO ₂ or the like as a mask.

  (E) Next, a material having polarization discontinuity with the GaN layer 12 is formed in an etched region in a direction perpendicular to the formed stripe pattern and horizontal to the sapphire substrate 100. For example, an AlGaN layer 14 may be formed on the m-plane GaN layer 12 as shown in FIG. As a result, a plurality of 2DEG layers can be formed at the interface between the m-plane GaN layer 12 and the AlGaN layer 14 as shown in FIG.

  In addition, PZT is formed on Pt by a sol-gel method or the like, a line and space structure is formed by a lithography method, PZT is etched using the resist as a mask, and the resist is peeled off. Thereafter, a method of forming a material in which polarization discontinuity occurs in a region where PZT is etched may be used. In the case of spin coating or sol-gel method, there is also an advantage that the process is simple. When spin coating or sol-gel method is used, different materials can be stacked in the direction perpendicular to the substrate, and n-type / p-type can be stacked in the direction perpendicular to the substrate surface.

  Also in the seventh embodiment, the trade-off between Seebeck coefficient and carrier concentration and the trade-off between Seebeck coefficient and electric conductivity can be improved, and a thermoelectric conversion element that can be stacked with high electric conductivity can be provided. .

  Also in the seventh embodiment, the trade-off in which the Seebeck coefficient S decreases as the carrier concentration n increases is not only solved by using the V-shaped recovery phenomenon of the Seebeck coefficient S, but can also be stacked. By forming a polarization discontinuity in a certain polarization material and laminating it, it is possible to provide a thermoelectric conversion element that solves the trade-off between the Seebeck coefficient S and the electrical conductivity σ and realizes a high dimensionless figure of merit ZT. .

  Also in the seventh embodiment, when a laminated structure is used, a thermoelectric conversion element that further improves electric conductivity σ is provided by forming both n-type and p-type in one element. Can do.

(Thermoelectric converter)
A thermoelectric generator can be provided by using the thermoelectric conversion elements according to the first to seventh embodiments. It is also possible to provide a thermoelectric generator capable of increasing the output by connecting a plurality of thermoelectric conversion elements according to the first to seventh embodiments in series.

An explanatory diagram of the operation principle of the thermoelectric generator 400A according to the basic technology is expressed as shown in FIG. 17A, and the output current I _O -output voltage V _O characteristic example of the thermoelectric generator 400A at the temperature change ΔT is It is expressed as shown in FIG.

As shown in FIG. 17A, the thermoelectric generator 400A according to the basic technology includes a coupling electrode 30 disposed on the high temperature (temperature T _h ) side and an n-side electrode 32 disposed on the low temperature (temperature T _c ) side. N-type semiconductor 28 disposed between the p-type semiconductor 26 disposed between the coupling electrode 30 disposed on the high temperature side and the p-side electrode 34 disposed on the low-temperature side, and the n-side electrode 32. And a load 36 connected between the p-side electrode 34. The electrons (e) in the n-type semiconductor 28 are conducted in the direction from the coupling electrode 30 disposed on the high temperature side to the n-side electrode 32 disposed on the low temperature side, as indicated by an arrow, and in the p-type semiconductor 26. The holes (h) are conducted in the direction from the coupling electrode 30 disposed on the high temperature side to the p-side electrode 34 disposed on the low temperature side, as indicated by an arrow. The temperature difference ΔT = T _h −T _c . As a result, the current I is conducted in the direction indicated by the arrow through the load 36, the n-type semiconductor 28, and the p-type semiconductor 26 that are connected in series in circuit. The operating point is determined by the intersection of the load characteristic determined by the load 36 and the conduction current I and the TEG 10 output current I _O -output voltage V _O characteristic example at the temperature change ΔT shown in FIG.

  18 is a schematic configuration example of the thermoelectric generator 400A according to the basic technology, and an example including the heat sink 38 on the low temperature side and the heat exchanger 40 on the high temperature side is expressed as shown in FIG. Further, a high temperature side heat transfer member 44 is disposed between the coupling electrode 30 and the heat exchanger 40, and a low temperature side heat transfer member 42 is disposed between the n side electrode 32 and the p side electrode 34 and the heat sink 38. Also good. By coupling the load 36 between the n-side electrode 32 and the p-side electrode 34 via the wiring 45, the current I is conducted to the load 36 in the direction indicated by the arrow.

  FIG. 19 shows an example of a schematic configuration of the thermoelectric power generation apparatus 400A according to the basic technology, in which a plurality of thermoelectric conversion elements are arranged in series.

Thermoelectric generator 400A according to the basic technique, as shown in FIG. 19, a high temperature (temperature T _h) a plurality of coupling electrodes _{30 1 · 30 2 · ... ·} 30 n and low temperature is disposed in the side (temperature T _c) side a plurality of n-side electrodes 32 _1, 32 _2, ..., 32 a plurality of n-type semiconductor 28 disposed between the _{n 1-28 2,} ..., 28 _n arranged in a plurality arranged in a high temperature side a plurality of p-type semiconductor 26 _1-disposed between the coupling electrode _{30 1 · 30 2 · ... ·} 30 n and a plurality of p-side electrode _{34 1 · 34 2 · ... ·} 34 n disposed on the low temperature side 26 comprises _2, ..., and 26 _n, and a load 36 connected between the n-side electrode 32 _n and p-side electrode 34 _1. The electrodes (32 ₁ , 34 ₂ ), (32 ₂ , 34 ₃ ),..., (32 _n−1 , 34 _n ) arranged adjacent to each other on the low temperature side are connected as a common electrode. The temperature difference ΔT = T _h −T _c . As a result, the circuit in series connected load 36 · n-type semiconductor _{28 1 · 28 2 · ... ·} 28 n · p -type semiconductor _{26 1 · 26 2 · ... ·} 26 n, in the direction indicated by the arrow Current I is conducted.

  As shown in FIG. 19, the thermoelectric power generation apparatus 400A according to the basic technology can increase the withstand voltage of the thermoelectric conversion module by arranging a plurality of TEGs in series. Also, it is possible to increase the amount of current and output by parallelizing the serial arrangement arrangement.

(Peltier device)
The thermoelectric conversion device using the thermoelectric conversion elements according to the first to seventh embodiments can convert the thermal energy accompanying the temperature difference between the first electrode 12 and the second electrode 14 into electric energy. The electric energy generated by applying a current between the first electrode and the second electrode can be converted into a temperature difference. Therefore, a Peltier device can be provided using the thermoelectric conversion elements according to the first to seventh embodiments.

  It is also possible to provide a Peltier device capable of producing a high temperature difference by connecting a plurality of thermoelectric conversion elements according to the first to seventh embodiments in series.

[Eighth embodiment]
In the thermoelectric generator 400 according to the eighth embodiment, a schematic upper surface configuration is represented as shown in FIG. 20 (a), and a schematic bird's-eye view configuration is represented as shown in FIG. 20 (b). Is done.

  As shown in FIGS. 20 (a) and 20 (b), the thermoelectric generator 400 according to the eighth embodiment includes a plurality of layers having a laminated structure having two or more electrically conductive layers (2DEG, 2DHG). It has a configuration in which thermoelectric conversion elements 10A, 10B, and 10C are connected in series.

The thermoelectric conversion elements 10A, 10B, and 10C applied to the thermoelectric power generation apparatus 400 according to the eighth embodiment include a sapphire substrate 100 and a sapphire substrate 100, as shown in FIGS. 20 (a) and 20 (b). and GaN layer _{12 1 a · 12 1 B ·} 12 1 C disposed above, AlGaN layer _{14 1 a · 14 1 B ·} 14 1 disposed on the GaN layer _{12 1 a · 12 1 B ·} 12 on ₁ C C, and the GaN layers 12 ₂ A, 12 ₂ B, 12 ₂ C and the GaN layers 12 ₂ A, 12 ₂ B, 12 ₂ C disposed on the AlGaN layers 14 ₁ A, 14 ₁ B, 14 ₁ C AlGaN layer 14 ₂ A · 14 ₂ B · 14 ₂ C disposed on the substrate.

Further, a 2DEG layer formed at the interface between the GaN layer 12 ₁ A · 12 ₁ B · 12 ₁ C and the AlGaN layer 14 ₁ A · 14 ₁ B · 14 ₁ C, and the AlGaN layer 14 ₁ A · 14 ₁ B · 2DHG layer formed at the interface between 14 ₁ C and GaN layer 12 ₂ A · 12 ₂ B · 12 ₂ C, GaN layer 12 ₂ A · 12 ₂ B · 12 ₂ C and AlGaN layer 14 ₂ A · 14 ₂ B A 2DEG layer formed at the interface with 14 ₂ C is provided.

  In addition, the first electrodes 16A, 16B, and 16C and the second electrodes 18A, 18B, and 18C are disposed on the side wall portion of the stacked structure and are in ohmic contact with the 2DEG layer. Here, the first electrodes 16A, 16B, and 16C and the second electrodes 18A, 18B, and 18C are not in ohmic contact with the 2DHG layer at the side wall portion, and are in Schottky contact, for example. For this reason, the carriers that contribute to the conduction of the thermoelectric conversion elements 10A, 10B, and 10C applied to the thermoelectric power generation apparatus 400 according to the eighth embodiment are electrons that conduct the 2DEG layer.

  Also, the main electrode 32A coupled to the first electrode 16A, the coupling electrode 30AB coupling the second electrodes 18A and 18B, the coupling electrode 30BC coupling the first electrodes 16B and 16C, and the second electrode 18C Main electrode 32C to be coupled.

  Although not shown, a load is connected between the main electrodes 32A and 32C, and the first electrodes 16A, 16B, and 16C are arranged in, for example, COLD SIDE, and the second electrodes 18A, 18B, and 18C are arranged in, for example, HOT SIDE. A thermoelectric generator 400 having a configuration in which a plurality of thermoelectric conversion elements 10A, 10B, and 10C are connected in series is obtained.

  The plurality of thermoelectric conversion elements 10A, 10B, and 10C are further multilayered, and films are stacked so that polarization discontinuity occurs like AlGaN / GaN / AlGaN / GaN / AlGaN / GaN / AlGaN / GaN / ... GaN / substrate. Thus, the 2DEG layer, the 2DHG layer, or both are formed at each AlGaN / GaN interface, whereby the electrical conductivity σ can be increased.

  Since it is important that polarization discontinuity occurs, a thermoelectric conversion element having a laminated structure of AlInN / GaN or a laminated structure such as AlGaN / GaAs / Si / AlGaN may be applied.

  Moreover, you may apply the thermoelectric conversion element provided with the laminated structure which combined them like AlGaN / GaN / AlInN / GaN /.../ board | substrate.

  Moreover, according to the eighth embodiment, it is also possible to provide a thermoelectric power generator capable of increasing output by connecting a plurality of thermoelectric conversion elements disclosed in any of the above embodiments in series. Is possible.

[Ninth embodiment]
In the thermoelectric generator 400 according to the ninth embodiment, a schematic top surface configuration is represented as shown in FIG. 21 (a), and a schematic bird's-eye view configuration is represented as shown in FIG. 21 (b). Is done.

  As shown in FIGS. 21 (a) and 21 (b), the thermoelectric generator 400 according to the ninth embodiment includes a plurality of laminated structures having two or more electrically conductive layers (2DEG, 2DHG). It has a configuration in which thermoelectric conversion elements 10A, 10B, and 10C are connected in series.

Thermoelectric conversion elements 10A, 10B, and 10C applied to the thermoelectric power generation apparatus 400 according to the ninth embodiment include a sapphire substrate 100 and a sapphire substrate 100, as shown in FIGS. 21 (a) and 21 (b). and GaN layer _{12 1 a · 12 1 B ·} 12 1 C disposed above, AlGaN layer _{14 1 a · 14 1 B ·} 14 1 disposed on the GaN layer _{12 1 a · 12 1 B ·} 12 on ₁ C C, and the GaN layers 12 ₂ A, 12 ₂ B, 12 ₂ C and the GaN layers 12 ₂ A, 12 ₂ B, 12 ₂ C disposed on the AlGaN layers 14 ₁ A, 14 ₁ B, 14 ₁ C AlGaN layer 14 ₂ A · 14 ₂ B · 14 ₂ C disposed on the substrate.

Further, a 2DEG layer formed at the interface between the GaN layer 12 ₁ A · 12 ₁ B · 12 ₁ C and the AlGaN layer 14 ₁ A · 14 ₁ B · 14 ₁ C, and the AlGaN layer 14 ₁ A · 14 ₁ B · 2DHG layer formed at the interface between 14 ₁ C and GaN layer 12 ₂ A · 12 ₂ B · 12 ₂ C, GaN layer 12 ₂ A · 12 ₂ B · 12 ₂ C and AlGaN layer 14 ₂ A · 14 ₂ B A 2DEG layer formed at the interface with 14 ₂ C is provided.

  Further, the first electrodes 16AE, 16BE, and 16CE and the second electrodes 18AE, 18BE, and 18CE that are disposed on the side wall portion of the stacked structure and are in ohmic contact with the 2DEG layer on the side wall portion, and the first electrode that is in ohmic contact with the 2DHG layer on the side wall portion. Electrodes 16AH, 16BH, and 16CH and second electrodes 18AH, 18BH, and 18CH are provided. For this reason, carriers that contribute to the conduction of the thermoelectric conversion elements 10A, 10B, and 10C applied to the thermoelectric generator 400 according to the ninth embodiment are electrons that conduct the 2DEG layer and holes that conduct the 2DHG. .

  Further, the main electrode 32A coupled to the first electrodes 16AE and 16AH, the coupling electrode 30AB coupling the second electrodes 18AE and 18AH and the second electrodes 18BE and 18BH, the first electrodes 16BE and 16BH, and the first electrode 16CE. A coupling electrode 30BC that couples 16CHs and a main electrode 32C coupled to the second electrodes 18CE and 18CH are provided.

  Although not shown, a load is connected between the main electrodes 32A and 32C, and the first electrodes 16AE, 16AH, 16BE, 16BH, 16CE, and 16CH are, for example, COLD SIDE, and the second electrodes 18AE, 18AH, 18BE, 18BH, By arranging 18CE · 18CH in, for example, HOT SIDE, a thermoelectric generator 400 having a configuration in which a plurality of thermoelectric conversion elements 10A, 10B, and 10C are connected in series is obtained.

  The plurality of thermoelectric conversion elements 10A, 10B, and 10C are further multilayered, and films are stacked so that polarization discontinuity occurs like AlGaN / GaN / AlGaN / GaN / AlGaN / GaN / AlGaN / GaN / ... GaN / substrate. Thus, the 2DEG layer, the 2DHG layer, or both are formed at each AlGaN / GaN interface, whereby the electrical conductivity σ can be increased.

  Since it is important that polarization discontinuity occurs, a thermoelectric conversion element having a laminated structure of AlInN / GaN or a laminated structure such as AlGaN / GaAs / Si / AlGaN may be applied.

  Moreover, you may apply the thermoelectric conversion element provided with the laminated structure which combined them like AlGaN / GaN / AlInN / GaN /.../ board | substrate.

  Further, the thermoelectric conversion elements 10A, 10B, and 10C applied to the thermoelectric power generation apparatus 400 according to the ninth embodiment can form both the 2DEG layer and the 2DHG layer, and can contribute to both conduction. Therefore, both p-type and n-type thermoelectric conversion elements can be formed with one element.

  Moreover, according to the ninth embodiment, it is also possible to provide a thermoelectric power generator capable of increasing output by connecting a plurality of thermoelectric conversion elements disclosed in any of the above embodiments in series. Is possible.

[Tenth embodiment]
In the thermoelectric generator 400 according to the tenth embodiment, a schematic upper surface configuration is represented as shown in FIG. 22 (a), and a schematic bird's-eye view configuration is represented as shown in FIG. 22 (b). Is done.

  As shown in FIGS. 22A and 22B, the thermoelectric power generation apparatus 400 according to the tenth embodiment includes a plurality of laminated structures having two or more electrically conductive layers (2DEG, 2DHG). It has a configuration in which thermoelectric conversion elements 10A, 10B, and 10C are connected in series.

The thermoelectric conversion elements 10A, 10B, and 10C applied to the thermoelectric power generation apparatus 400 according to the tenth embodiment include a sapphire substrate 100 and a sapphire substrate 100, as shown in FIGS. 22 (a) and 22 (b). and GaN layer _{12 1 a · 12 1 B ·} 12 1 C disposed above, AlGaN layer _{14 1 a · 14 1 B ·} 14 1 disposed on the GaN layer _{12 1 a · 12 1 B ·} 12 on ₁ C C, and the GaN layers 12 ₂ A, 12 ₂ B, 12 ₂ C and the GaN layers 12 ₂ A, 12 ₂ B, 12 ₂ C disposed on the AlGaN layers 14 ₁ A, 14 ₁ B, 14 ₁ C AlGaN layer 14 ₂ A · 14 ₂ B · 14 ₂ C disposed on the substrate.

Further, a 2DEG layer formed at the interface between the GaN layer 12 ₁ A · 12 ₁ B · 12 ₁ C and the AlGaN layer 14 ₁ A · 14 ₁ B · 14 ₁ C, and the AlGaN layer 14 ₁ A · 14 ₁ B · 2DHG layer formed at the interface between 14 ₁ C and GaN layer 12 ₂ A · 12 ₂ B · 12 ₂ C, GaN layer 12 ₂ A · 12 ₂ B · 12 ₂ C and AlGaN layer 14 ₂ A · 14 ₂ B A 2DEG layer formed at the interface with 14 ₂ C is provided.

  In addition, the first electrodes 16AE and 16CE and the second electrodes 18AE and 18CE that are disposed on the side wall portion of the stacked structure and are in ohmic contact with the 2DEG layer on the side wall portion, the first electrode 16BH and the second electrode that are in ohmic contact with the 2DHG layer on the side wall portion 2 electrodes 18BH. Here, the first electrodes 16AE and 16CE and the second electrodes 18AE and 18CE are not in ohmic contact with the 2DHG layer at the side wall portion, and are in Schottky contact, for example. The first electrode 16BH and the second electrode 18BH are not in ohmic contact with the 2DEG layer at the side wall portion, and are in Schottky contact, for example.

  Therefore, the carriers that contribute to the conduction of the thermoelectric conversion elements 10A and 10C applied to the thermoelectric power generation apparatus 400 according to the tenth embodiment are electrons that conduct the 2DEG layer, and contribute to the conduction of the thermoelectric conversion element 10B. The carriers to be carried are holes that conduct through the 2DHG layer.

  Also, a main electrode 32A coupled to the first electrode 16AE, a coupling electrode 30AB coupling the second electrode 18AE and the second electrode 18BH, and a coupling electrode 30BC coupling the first electrode 16BH and the first electrode 16CE And a main electrode 32C coupled to the second electrode 18CE.

  Although not shown, a load is connected between the main electrodes 32A and 32C, and the first electrodes 16AE, 16BH, and 16CE are arranged in, for example, COLD SIDE, and the second electrodes 18AE, 18BH, and 18CE are arranged in, for example, HOT SIDE. A thermoelectric generator 400 having a configuration in which a plurality of thermoelectric conversion elements 10A, 10B, and 10C are connected in series is obtained.

  The plurality of thermoelectric conversion elements 10A, 10B, and 10C are further multilayered, and films are stacked so that polarization discontinuity occurs like AlGaN / GaN / AlGaN / GaN / AlGaN / GaN / AlGaN / GaN / ... GaN / substrate. Thus, the 2DEG layer, the 2DHG layer, or both are formed at each AlGaN / GaN interface, whereby the electrical conductivity σ can be increased.

  Since it is important that polarization discontinuity occurs, a thermoelectric conversion element having a laminated structure of AlInN / GaN or a laminated structure such as AlGaN / GaAs / Si / AlGaN may be applied.

  Moreover, you may apply the thermoelectric conversion element provided with the laminated structure which combined them like AlGaN / GaN / AlInN / GaN /.../ board | substrate.

  Further, according to the tenth embodiment, it is also possible to provide a thermoelectric power generator capable of increasing the output by connecting a plurality of thermoelectric conversion elements disclosed in any of the above embodiments in series. Is possible.

  According to the present embodiment, the trade-off in which the Seebeck coefficient S decreases as the carrier concentration n increases can be solved as well as stacked by using the V-shaped recovery phenomenon of the Seebeck coefficient S. By forming and discontinuating polarization discontinuity in a polarization material, the trade-off between the Seebeck coefficient S and the electrical conductivity σ is also solved, and a thermoelectric conversion element that achieves a high dimensionless figure of merit ZT and the thermoelectric conversion element are used. The thermoelectric power generation apparatus that has been provided can be provided.

  According to the present embodiment, when a laminated structure is used, a thermoelectric conversion element that further improves electric conductivity σ by forming both n-type and p-type in one element, and this A thermoelectric power generator using a thermoelectric conversion element can be provided.

  As described above, according to the present embodiment, the trade-off between the carrier concentration and the Seebeck coefficient, and the trade-off between the Seebeck coefficient and the electrical conductivity are improved, and the thermoelectric conversion element that can be stacked with high electrical conductivity and A thermoelectric generator and a Peltier device using this thermoelectric conversion element can be provided.

[Other embodiments]
Although the embodiment has been described as described above, it should be understood that the discussion and the drawings that form a part of this disclosure are illustrative and do not limit the embodiment. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  As described above, this embodiment includes various embodiments not described here.

  The thermoelectric conversion element and the thermoelectric power generation apparatus of the present embodiment are applied to an apparatus and system that efficiently supplies energy generated by the thermoelectric conversion element such as a thermoelectric power generation system, and are applied to mobile devices, in-vehicle devices, industrial devices, medical devices, and the like. Applicable to a wide range of fields. In addition, in the Peltier device to which the thermoelectric conversion element according to the present embodiment is applied, it is applied to a device and a system that efficiently convert input energy into a temperature difference, such as a mobile device, an in-vehicle device, an industrial device, and a medical device. Applicable to a wide range of fields.

8 ... Silicon substrates 10, 10A, 10B, 10C ... Thermoelectric conversion elements 11 ... GaN templates 12, 12 ₁ , 12 ₂ , 12 ₃ , 12 ₄ ... First material layer (GaN layer)
13... AlN layer 14, 14 ₁ , 14 ₂ , 14 ₃ , 14 ₄ , 14A, 14B, 14C ... second material layer (AlGaN layer)
16, 16 ₁ , 16 ₂ , 16A, 16B, 16C, 16AE, 16BE, 16CE, 16AH, 16BH, 16CH ... Electrode (COLD SIDE)
18, 18 ₁ , 18 ₂ , 18A, 18B, 18C, 18AE, 18BE, 18CE, 18AH, 18BH, 18CH ... electrode (HOT SIDE)
20 ₁ , 20 ₂ ... polarization material layers 20A, 20B ... material layers 22, 22A, 22B ... voltage probes 24, 24A, 24B ... thermocouples 26, 26 ₁ , 26 ₂ , ..., 26 _n ... p-type semiconductors 28, 28 _{1, 28 2, ..., 28} n ... n -type semiconductor 30,30AB, 30BC ... coupling electrodes _{32,32 1, 32 2, ...,} 32 n ... n -side electrode 32A, 32C ... main electrodes 34 _1, 34 ₂ , ... 34 _n ... p-side electrode 36 ... load 38 ... heat sink 40 ... heat exchanger 42, 44 ... heat transfer member 45 ... wiring 100 ... sapphire substrate 200 ... heat sink 300 ... heater 400A, 400 ... thermoelectric generator ΔT ... Temperature change (temperature difference)
I _O ... output current V _O ... output voltage μ ... mobility n ... carrier concentration σ ... electrical conductivity S ... Seebeck coefficient ZT ... dimensionless figure of merit κ ... thermal conductivity

Claims (23)

A first material layer;
A second material layer disposed in contact with the first material layer;
A first electrode electrically connected to the first material layer and the second material layer;
A second electrode electrically connected to the first material layer and the second material layer and spaced apart from the first electrode ;
A substrate on which a unit structure is formed by the first material layer and the second material layer,
At the interface between the first material layer and the second material layer, there is an electric conductive layer mainly responsible for electric conduction due to discontinuous electric polarization between the first material layer and the second material layer. Occur,
The first electrode and the second electrode are electrically connected to the electrically conductive layer when the electrically conductive layer is generated,
The difference in electrical polarization at the interface between the first material layer and the second material layer is set to have a relationship such that the Seebeck coefficient of the electrically conductive layer increases as the reduced Fermi energy increases,
The unit structure of the first material layer and the second material layer is formed over a plurality of layers so that the interface between the first material layer and the second material layer and the surface of the substrate are perpendicular to each other. The thermoelectric conversion element characterized by the above-mentioned.   The thermoelectric conversion element according to claim 1, wherein the second material layer includes a semiconductor. The first material layer is made of Al. _a Ga _b In _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1),
  The second material layer has an Al composition different from that of the first material layer. _c Ga _d In _1-cd The thermoelectric conversion element according to claim 1, comprising N (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, 0 ≦ c + d ≦ 1). The thermoelectric conversion element according to claim 3, wherein the first material layer includes a GaN layer, and the second material layer includes an AlGaN layer.   The thermoelectric conversion element according to claim 2, wherein the second material layer does not contain N.   The thermoelectric conversion element according to claim 1, wherein the first material layer includes a ferroelectric.   The electric conductive layer includes a two-dimensional electron gas layer, a two-dimensional hole gas layer, or both a two-dimensional electron gas layer and a two-dimensional hole gas layer. The thermoelectric conversion element according to item.   8. The first material layer and the second material layer are not doped for the purpose of conductivity modulation of a two-dimensional electron gas layer or a two-dimensional hole gas layer. The thermoelectric conversion element of any one of these.   In the direction perpendicular to the interface between the first material layer and the second material layer, a layer which is not necessarily the same layer structure and mainly responsible for electrical conduction is sandwiched between the first material layer and the second material layer. The thermoelectric conversion element according to claim 1, wherein the unit structure is repeatedly laminated.   The thermoelectric conversion element according to claim 1, wherein a substrate on which the first material layer and the second material layer are formed contains silicon.   The thermoelectric conversion element according to any one of claims 1 to 9, wherein the substrate on which the first material layer and the second material layer are formed contains sapphire.   The thermoelectric conversion element according to claim 1, wherein the first electrode and the second electrode are formed in contact with the electric conductive layer.   The thermoelectric conversion element according to any one of claims 1 to 9, wherein the first electrode and the second electrode are in ohmic contact with the electric conductive layer.   The thermoelectric conversion element according to claim 1, wherein the first electrode and the second electrode are connected to the second material layer.   The thermoelectric conversion element according to claim 1, wherein the first electrode and the second electrode are made of the same material. A first material layer;
A second material layer disposed in contact with the first material layer;
A first electrode electrically connected to the first material layer and the second material layer;
A second electrode electrically connected to the first material layer and the second material layer and spaced apart from the first electrode;
A substrate on which a unit structure is formed by the first material layer and the second material layer,
At the interface between the first material layer and the second material layer, there is an electric conductive layer mainly responsible for electric conduction due to discontinuous electric polarization between the first material layer and the second material layer. Occur,
The first electrode and the second electrode are electrically connected to the electric conductive layer when the electric conductive layer is generated,
The difference in electrical polarization at the interface between the first material layer and the second material layer is set so that the Seebeck coefficient of the electrically conductive layer increases as the carrier concentration of the electrically conductive layer increases. And
The unit structure of the first material layer and the second material layer is formed over a plurality of layers so that the interface between the first material layer and the second material layer and the surface of the substrate are perpendicular to each other. The thermoelectric conversion element characterized by the above-mentioned. A first material layer;
A second material layer disposed in contact with the first material layer;
A first electrode electrically connected to the first material layer and the second material layer;
A second electrode electrically connected to the first material layer and the second material layer and spaced apart from the first electrode;
A substrate on which a unit structure formed of the first material layer and the second material layer is formed. The interface between the first material layer and the second material layer includes the first material layer and the second material layer. An electric conduction layer mainly responsible for electric conduction is generated due to discontinuous electric polarization with the material layer,
The first electrode and the second electrode are electrically connected to the electrically conductive layer when the electrically conductive layer is generated,
The difference in electric polarization at the interface between the first material layer and the second material layer is set so that the dimensionless figure of merit of the electrically conductive layer increases as the carrier concentration of the electrically conductive layer increases. Has been
The unit structure of the first material layer and the second material layer is formed over a plurality of layers so that the interface between the first material layer and the second material layer and the surface of the substrate are perpendicular to each other. The thermoelectric conversion element characterized by the above-mentioned.   A thermoelectric power generation apparatus comprising the thermoelectric conversion element according to claim 1.   The thermoelectric power generator according to claim 18, wherein a plurality of the thermoelectric conversion elements are connected in series.   A Peltier device comprising the thermoelectric conversion element according to claim 1.   The Peltier device according to claim 20, wherein a plurality of the thermoelectric conversion elements are connected in series. It is a manufacturing method of the thermoelectric conversion element given in any 1 paragraph of Claims 1-4 , 16 , and 17 ,
Preparing the substrate for forming the first material layer and the second material layer;
Al _a Ga _b In _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1) layer on the substrate forming the first material layer and the second material layer Forming a step;
The _{Al a Ga b In 1-a} -b N (0 ≦ a ≦ 1,0 ≦ b ≦ 1,0 ≦ a + b ≦ 1) Al on the layer _{c Ga d In 1-c-} d N (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, 0 ≦ c + d ≦ 1) forming a layer;
The Al _a Ga _b In _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1) layer and the Al _c Ga _d In _1-cd N (0 ≦ c ≦ And 1. 0 ≦ d ≦ 1, 0 ≦ c + d ≦ 1) etching the layer. A method for manufacturing a thermoelectric conversion element, comprising: It is a manufacturing method of the thermoelectric conversion element given in any 1 paragraph of Claims 1-4 , 16 , and 17 ,
Preparing the substrate for forming the first material layer and the second material layer;
An Al _a Ga _b In ₁ -abN (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1) layer is formed on the substrate on which the first material layer and the second material layer are formed. Forming, and
The _{Al a Ga b In 1-a} -b N (0 ≦ a ≦ 1,0 ≦ b ≦ 1,0 ≦ a + b ≦ 1) Al on the layer _{c Ga d In 1-c-} d N (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, 0 ≦ c + d ≦ 1) forming a layer;
The Al _a Ga _b In _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1) layer and the Al _c Ga _d In _1-cd N (0 ≦ c ≦ 1. 0 ≦ d ≦ 1, 0 ≦ c + d ≦ 1) A step of forming a region in which an electrode is formed by opening a wall, and a method for manufacturing a thermoelectric conversion element.

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