JP2013016685A - Thermoelectric conversion material, thermoelectric conversion element, and method for manufacturing the same - Google Patents

Thermoelectric conversion material, thermoelectric conversion element, and method for manufacturing the same Download PDF

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JP2013016685A
JP2013016685A JP2011149055A JP2011149055A JP2013016685A JP 2013016685 A JP2013016685 A JP 2013016685A JP 2011149055 A JP2011149055 A JP 2011149055A JP 2011149055 A JP2011149055 A JP 2011149055A JP 2013016685 A JP2013016685 A JP 2013016685A
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semiconductor layer
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Ken Kurosaki
健 黒崎
Tirayut Phadepin
ティラユット プァーデビン
Adul Hanwangmong
アドゥル ハンワングモング
Yuji Oishi
佑治 大石
Hiroaki Muta
浩明 牟田
Shinsuke Yamanaka
伸介 山中
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Osaka University NUC
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Abstract

PROBLEM TO BE SOLVED: To provide a thermoelectric conversion element constituted of a novel material.SOLUTION: A thermoelectric conversion element (10) according to the present invention includes an n-type semiconductor layer (20n) and a p-type semiconductor layer (20p). The p-type semiconductor layer (20p) contains at least one selected from a group consisting of CuGaTe, CuGaTe, CuGaTe, and CuGaTe. The thermoelectric conversion element (10) is suitably used at a temperature of 800 K or higher. For example, it is preferable that the p-type semiconductor layer (20p) contains CuGaTe.

Description

本発明は、熱電変換材料、熱電変換素子およびその作製方法に関する。   The present invention relates to a thermoelectric conversion material, a thermoelectric conversion element, and a manufacturing method thereof.

近年、熱と電気とを相互に変換可能な熱電変換モジュールが注目されている。一般に、動力発生源で動力を発生させる際に発生した熱の大部分は棄てられてしまう。例えば、自動車のエンジンで発生したエネルギーのうち動力として取り出せるのは約３０％であり、残りの約７０％は熱として廃棄されてしまう。このため、発生した熱の有効利用を図ることが検討されている。   In recent years, thermoelectric conversion modules that can convert heat and electricity to each other have attracted attention. Generally, most of the heat generated when power is generated by a power generation source is discarded. For example, about 30% of the energy generated in the engine of a car can be extracted as power, and the remaining about 70% is discarded as heat. For this reason, it has been studied to effectively use the generated heat.

一般に、熱電変換素子の効率は性能指数ＺＴで表され、性能指数の向上が図られている（例えば、特許文献１参照）。特許文献１には、超格子構造を有する熱電効果素子が記載されている。特許文献１に記載の熱電効果素子は、２種類以上のターゲットに照射するイオンビームを調整することにより、異なる層を交互に積層させている。   In general, the efficiency of a thermoelectric conversion element is represented by a figure of merit ZT, and the figure of merit is improved (see, for example, Patent Document 1). Patent Document 1 describes a thermoelectric effect element having a superlattice structure. In the thermoelectric effect element described in Patent Document 1, different layers are alternately stacked by adjusting an ion beam applied to two or more types of targets.

特開２００７−０１２９８０号公報JP 2007-012980 A

しかしながら、特許文献１の熱電効果素子では、超格子構造を形成する必要があり、このような熱電効果素子を簡便に作製することは困難である。また、比較的簡便に作製可能な熱電変換素子は充分な変換効率を示さない。   However, in the thermoelectric effect element of Patent Document 1, it is necessary to form a superlattice structure, and it is difficult to easily manufacture such a thermoelectric effect element. In addition, thermoelectric conversion elements that can be manufactured relatively simply do not exhibit sufficient conversion efficiency.

本発明は上記課題を鑑みてなされたものであり、その目的は、新規な熱電変換材料、および、このような熱電変換材料を含む熱電変換素子およびその作製方法を提供することにある。   This invention is made | formed in view of the said subject, The objective is to provide the novel thermoelectric conversion material, the thermoelectric conversion element containing such a thermoelectric conversion material, and its manufacturing method.

本発明による熱電変換素子は、ｎ型半導体層と、ｐ型半導体層とを備える、熱電変換素子であって、前記ｐ型半導体層は、ＣｕＧａＴｅ２、Ｃｕ３Ｇａ５Ｔｅ９、ＣｕＧａ３Ｔｅ５およびＣｕＧａ５Ｔｅ８からなる群から選択された少なくとも１つを含む。 The thermoelectric conversion element according to the present invention is a thermoelectric conversion element including an n-type semiconductor layer and a p-type semiconductor layer, and the p-type semiconductor layer includes CuGaTe 2 , Cu 3 Ga 5 Te 9 , and CuGa 3 Te 5. And at least one selected from the group consisting of CuGa 5 Te 8 .

ある実施形態において、前記熱電変換素子は、７００Ｋ以上、好ましくは８００Ｋ以上、より好ましくは９００Ｋ以上の温度下で用いられる。   In one embodiment, the thermoelectric conversion element is used at a temperature of 700K or higher, preferably 800K or higher, more preferably 900K or higher.

ある実施形態において、前記ｐ型半導体層は、ＣｕＧａＴｅ２を含む。 In one embodiment, the p-type semiconductor layer includes CuGaTe 2 .

ある実施形態において、前記熱電変換素子は、前記ｐ型半導体層と前記ｎ型半導体層のそれぞれと接触する電極をさらに備える。   In one embodiment, the thermoelectric conversion element further includes an electrode in contact with each of the p-type semiconductor layer and the n-type semiconductor layer.

本発明による熱電変換材料は、ＣｕＧａＴｅ２、Ｃｕ３Ｇａ５Ｔｅ９、ＣｕＧａ３Ｔｅ５およびＣｕＧａ５Ｔｅ８からなる群から選択された少なくとも１つを含む。 The thermoelectric conversion material according to the present invention includes at least one selected from the group consisting of CuGaTe 2 , Cu 3 Ga 5 Te 9 , CuGa 3 Te 5 and CuGa 5 Te 8 .

本発明による熱電変換素子の作製方法は、ｎ型半導体層を用意する工程と、ｐ型半導体層を用意する工程と、前記ｎ型半導体層および前記ｐ型半導体層を電気的に接続する工程とを包含し、前記ｐ型半導体層を用意する工程において、前記ｐ型半導体層はＣｕＧａＴｅ２、Ｃｕ３Ｇａ５Ｔｅ９、ＣｕＧａ３Ｔｅ５およびＣｕＧａ５Ｔｅ８からなる群から選択された少なくとも１つを含む。 The method for producing a thermoelectric conversion element according to the present invention includes a step of preparing an n-type semiconductor layer, a step of preparing a p-type semiconductor layer, and a step of electrically connecting the n-type semiconductor layer and the p-type semiconductor layer. In the step of preparing the p-type semiconductor layer, the p-type semiconductor layer is at least one selected from the group consisting of CuGaTe 2 , Cu 3 Ga 5 Te 9 , CuGa 3 Te 5 and CuGa 5 Te 8. including.

ある実施形態において、前記ｐ型半導体層を用意する工程は、化学量論的に所定の割合でＣｕ、ＧａおよびＴｅの存在する原料を用意し、上記原料の溶融を行う工程を含む。   In one embodiment, the step of preparing the p-type semiconductor layer includes a step of preparing a raw material containing Cu, Ga and Te in a stoichiometric predetermined ratio and melting the raw material.

ある実施形態では、前記ｐ型半導体層を用意する工程において、前記ｐ型半導体層はＣｕＧａＴｅ２を含む。 In one embodiment, in the step of preparing the p-type semiconductor layer, the p-type semiconductor layer includes CuGaTe 2 .

本発明によれば、新規な熱電変換材料、ならびに、このような熱電変換材料を含む熱電変換素子およびその作製方法を提供することができる。   ADVANTAGE OF THE INVENTION According to this invention, the novel thermoelectric conversion material, the thermoelectric conversion element containing such a thermoelectric conversion material, and its manufacturing method can be provided.

本発明による熱電変換素子の実施形態の模式図である。It is a schematic diagram of embodiment of the thermoelectric conversion element by this invention. ＣｕＧａＴｅ化合物のＸＲＤの結果を示すグラフである。It is a graph which shows the result of XRD of a CuGaTe compound. ＣｕＧａＴｅ化合物の電気抵抗率の温度依存性を示すグラフである。It is a graph which shows the temperature dependence of the electrical resistivity of a CuGaTe compound. ＣｕＧａＴｅ化合物のゼーベック係数の温度依存性を示すグラフである。It is a graph which shows the temperature dependence of the Seebeck coefficient of a CuGaTe compound. ＣｕＧａＴｅ化合物の熱伝導率の温度依存性を示すグラフである。It is a graph which shows the temperature dependence of the thermal conductivity of a CuGaTe compound. ＣｕＧａＴｅ化合物の性能指数の温度依存性を示すグラフである。It is a graph which shows the temperature dependence of the figure of merit of a CuGaTe compound.

以下、図面を参照して本発明による熱電変換材料、熱電変換素子およびその作製方法の実施形態を説明する。だだし、本発明は以下の実施形態に限定されない。   Hereinafter, embodiments of a thermoelectric conversion material, a thermoelectric conversion element, and a manufacturing method thereof according to the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments.

図１に、本発明による熱電変換素子の実施形態の模式図を示す。本実施形態の熱電変換素子１０は、ｎ型半導体層２０ｎと、ｐ型半導体層２０ｐとを備えている。本明細書の以下の説明においてｎ型半導体層２０ｎおよびｐ型半導体層２０ｐをそれぞれ半導体層２０ｎおよび半導体層２０ｐと呼ぶことがある。図１に示した熱電変換素子１０では、半導体層２０ｎおよび半導体層２０ｐは電極２２を介して電気的に接続されている。ここでは、電極２２は、半導体層２０ｐおよび半導体層２０ｎの両方の端部と接触している。また、図１に示したように、熱電変換素子１０は、半導体層２０ｐの他方の端部と電気的に接続された電極２４ａと、ｎ型半導体層２０ｎの他方の端部と電気的に接続された電極２４ｂとをさら備えていてもよい。   In FIG. 1, the schematic diagram of embodiment of the thermoelectric conversion element by this invention is shown. The thermoelectric conversion element 10 of this embodiment includes an n-type semiconductor layer 20n and a p-type semiconductor layer 20p. In the following description of this specification, the n-type semiconductor layer 20n and the p-type semiconductor layer 20p may be referred to as a semiconductor layer 20n and a semiconductor layer 20p, respectively. In the thermoelectric conversion element 10 shown in FIG. 1, the semiconductor layer 20 n and the semiconductor layer 20 p are electrically connected via an electrode 22. Here, the electrode 22 is in contact with both ends of the semiconductor layer 20p and the semiconductor layer 20n. As shown in FIG. 1, the thermoelectric conversion element 10 is electrically connected to the electrode 24a electrically connected to the other end of the semiconductor layer 20p and the other end of the n-type semiconductor layer 20n. The electrode 24b may be further provided.

電極２２の温度が電極２４ａ、２４ｂよりも高い場合、ゼーベック効果によって半導体層２０ｎおよび半導体層２０ｐ内をそれぞれ電子および正孔が移動し、これにより、電流を発生させることができる。このような電流を負荷Ｌに流すことにより、負荷Ｌに仕事をさせることができる。また、電極２２の温度が電極２４ａ、２４ｂよりも低い場合、電流は反対方向に流れる。   When the temperature of the electrode 22 is higher than that of the electrodes 24a and 24b, electrons and holes move in the semiconductor layer 20n and the semiconductor layer 20p, respectively, due to the Seebeck effect, whereby a current can be generated. By flowing such a current through the load L, the load L can be made to work. When the temperature of the electrode 22 is lower than that of the electrodes 24a and 24b, the current flows in the opposite direction.

あるいは、電極２４ｂから半導体層２０ｎ、電極２２、半導体層２０ｐおよび電極２４ａを通るように電流を流すことにより、電極２２で吸熱を行い、電極２４ａ、２４ｂで放熱を行うことができる。また、電極２４ａから半導体層２０ｐ、電極２２、半導体層２０ｎおよび電極２４ｂを通るように電流を流すことにより、電極２２で放熱を行い、電極２４ａ、２４ｂで吸熱を行うことができる。   Alternatively, by passing a current from the electrode 24b through the semiconductor layer 20n, the electrode 22, the semiconductor layer 20p, and the electrode 24a, the electrode 22 can absorb heat and the electrodes 24a and 24b can dissipate heat. Further, by passing a current from the electrode 24a through the semiconductor layer 20p, the electrode 22, the semiconductor layer 20n, and the electrode 24b, heat can be radiated from the electrode 22 and heat can be absorbed from the electrodes 24a and 24b.

例えば、電極２２、２４ａ、２４ｂは銀から形成され、電極２２、２４ａ、２４ｂは、絶縁基板（ここでは図示せず）によって支持されてもよい。絶縁基板として例えばセラミック基板（一例としてアルミナ基板）を用いてもよい。また、電極２４ａ、２４ｂは分離されているが、電極２４ａ、２４ｂを支持する絶縁基板は一体的に設けられてもよい。   For example, the electrodes 22, 24a, 24b may be made of silver, and the electrodes 22, 24a, 24b may be supported by an insulating substrate (not shown here). For example, a ceramic substrate (an alumina substrate as an example) may be used as the insulating substrate. In addition, although the electrodes 24a and 24b are separated, an insulating substrate that supports the electrodes 24a and 24b may be provided integrally.

本実施形態の熱電変換素子１０において、ｐ型半導体層２０ｐは本発明による熱電変換材料の実施形態から形成される。本実施形態の熱電変換材料は、ＣｕＧａＴｅ２、Ｃｕ３Ｇａ５Ｔｅ９、ＣｕＧａ３Ｔｅ５およびＣｕＧａ５Ｔｅ８からなる群から選択された少なくとも１つを含む。本明細書の以下の説明において、ＣｕＧａＴｅ２、Ｃｕ３Ｇａ５Ｔｅ９、ＣｕＧａ３Ｔｅ５およびＣｕＧａ５Ｔｅ８を総称してＣｕＧａＴｅ化合物と呼ぶことがある。性能指数の比較的高い半導体層２０ｐはバルク状のＣｕＧａＴｅ化合物から作製される。ＣｕＧａＴｅ化合物はカルコパイライト型結晶構造または閃亜鉛鉱型構造を有している。 In the thermoelectric conversion element 10 of the present embodiment, the p-type semiconductor layer 20p is formed from the embodiment of the thermoelectric conversion material according to the present invention. The thermoelectric conversion material of the present embodiment includes at least one selected from the group consisting of CuGaTe 2 , Cu 3 Ga 5 Te 9 , CuGa 3 Te 5 and CuGa 5 Te 8 . In the following description of the present specification, CuGaTe 2 , Cu 3 Ga 5 Te 9 , CuGa 3 Te 5 and CuGa 5 Te 8 may be collectively referred to as a CuGaTe compound. The semiconductor layer 20p having a relatively high figure of merit is manufactured from a bulk CuGaTe compound. The CuGaTe compound has a chalcopyrite type crystal structure or a zinc blende type structure.

なお、詳細は後述するが、半導体層２０ｐは、ＣｕＧａＴｅ２から形成されることが好ましい。これにより、性能指数の高いバルク状の半導体層２０ｐを形成することができる。性能指数は温度にも依存するが、温度が９００Ｋを超える場合、性能指数ＺＴを１．５よりも大きくすることができる。 Although the details will be described later, the semiconductor layer 20p is preferably formed from CuGaTe 2. Thereby, a bulk semiconductor layer 20p having a high figure of merit can be formed. The figure of merit also depends on the temperature, but if the temperature exceeds 900K, the figure of merit ZT can be greater than 1.5.

半導体層２０ｎは任意の材料から形成されてもよい。ただし、半導体層２０ｎの材料は、同一基板に、ｐ型半導体層２０ｐとともにｎ型半導体層２０ｎを作製可能なように選択されることが好ましい。例えば、添加する不純物を変更することにより、ｐ型半導体層２０ｐおよびｎ型半導体層２０ｎを別々に形成可能であることが好ましい。   The semiconductor layer 20n may be formed from any material. However, the material of the semiconductor layer 20n is preferably selected so that the n-type semiconductor layer 20n can be formed together with the p-type semiconductor layer 20p on the same substrate. For example, it is preferable that the p-type semiconductor layer 20p and the n-type semiconductor layer 20n can be formed separately by changing the impurity to be added.

本実施形態の熱電変換素子１０では熱電変換が効率的に行われる。上述したように、熱電変換素子１０の特性は性能指数で示される。性能指数ＺＴは、ＺＴ＝Ｓ２σＴ／κと表される。ここで、Ｓはゼーベック係数（ＶＫ−１）であり、σは電気伝導率（Ω−１ｍ−１）であり、Ｔは絶対温度（Ｋ）であり、κは熱伝導率（Ｗｍ−１Ｋ−１）である。なお、電気伝導率σは電気抵抗率ρの逆数であり、性能指数ＺＴはＺＴ＝Ｓ２Ｔ／ρκとも表される。例えば、熱電変換素子１０は８００Ｋ以上の温度下で用いられることが好ましく、９００Ｋ以上の温度下で用いられることがさらに好ましい。また、熱電変換素子１０は温度７００Ｋ以上の温度下で用いられてもよい。 In the thermoelectric conversion element 10 of this embodiment, thermoelectric conversion is efficiently performed. As described above, the characteristics of the thermoelectric conversion element 10 are indicated by a figure of merit. The figure of merit ZT is expressed as ZT = S 2 σT / κ. Here, S is the Seebeck coefficient (VK −1 ), σ is the electrical conductivity (Ω −1 m −1 ), T is the absolute temperature (K), and κ is the thermal conductivity (Wm −1). K −1 ). The electrical conductivity σ is the reciprocal of the electrical resistivity ρ, and the figure of merit ZT is also expressed as ZT = S 2 T / ρκ. For example, the thermoelectric conversion element 10 is preferably used at a temperature of 800K or higher, and more preferably at a temperature of 900K or higher. Moreover, the thermoelectric conversion element 10 may be used under the temperature of 700K or more.

ＣｕＧａＴｅ化合物は、例えば、以下のように作製される。まず、作製されるべきＣｕＧａＴｅ化合物に応じて、化学量論的に所定の割合でＣｕ、ＧａおよびＴｅの存在する原料を用意する。例えば、この原料は、Ｃｕ２ＴｅおよびＧａ２Ｔｅ３を所定の割合で含んでもよい。Ｃｕ２ＴｅおよびＧａ２ＴｅからＣｕＧａＴｅ２を形成する場合、Ｃｕ２ＴｅおよびＧａ２Ｔｅ３の割合は１：１である。なお、ここでは、原料は、Ｃｕ２ＴｅおよびＧａ２Ｔｅ３を所定の割合で含んでいるが、原料は、Ｃｕ、ＧａおよびＴｅを個別に所定の割合で含んでもよく、または、Ｃｕ、Ｇａ２Ｔｅ３およびＴｅを所定の割合で含んでもよい。 A CuGaTe compound is produced as follows, for example. First, in accordance with the CuGaTe compound to be produced, a raw material containing Cu, Ga and Te in a stoichiometrically predetermined ratio is prepared. For example, this raw material may contain Cu 2 Te and Ga 2 Te 3 in a predetermined ratio. When forming the CuGaTe 2 from Cu 2 Te and Ga 2 Te, the ratio of Cu 2 Te and Ga 2 Te 3 is 1: 1. Here, the raw material includes Cu 2 Te and Ga 2 Te 3 in a predetermined ratio, but the raw material may individually include Cu, Ga, and Te in a predetermined ratio, or Cu, Ga 2 Te 3 and Te may be included in a predetermined ratio.

その後、上述した原料の溶融を行い、ＣｕＧａＴｅ化合物を形成する。例えば、Ｃｕ２ＴｅおよびＧａ２Ｔｅ３を石英管に真空封入して９００℃で１日溶融させた後、５００℃で３日間アニーリングする。アニーリングにより、石英管には溶融インゴット試料が形成される。 Thereafter, the raw materials described above are melted to form a CuGaTe compound. For example, Cu 2 Te and Ga 2 Te 3 are vacuum-sealed in a quartz tube, melted at 900 ° C. for 1 day, and then annealed at 500 ° C. for 3 days. By annealing, a molten ingot sample is formed in the quartz tube.

この溶融インゴット試料を石英管から取り出し、溶融インゴット試料を粉砕する。その後、アルゴン気流下において３時間、６００℃でホットプレスによって焼結する。これにより、バルク体の試料が得られる。その後、バルク体を切断、整形、研磨することにより、物性測定用の試料が得られる。   The molten ingot sample is taken out from the quartz tube, and the molten ingot sample is pulverized. Thereafter, sintering is performed by hot pressing at 600 ° C. for 3 hours under an argon stream. Thereby, the sample of a bulk body is obtained. Thereafter, the bulk body is cut, shaped, and polished to obtain a sample for measuring physical properties.

得られた試料の同定は、例えば、Ｘ線回折（Ｘ−Ｒａｙ Ｄｉｆｆｒａｃｔｉｏｎ：ＸＲＤ）を用いて行われる。例えば、１：１の割合でＣｕ２ＴｅおよびＧａ２Ｔｅ３を溶融させた場合、ＸＲＤから、得られたバルク体がＣｕＧａＴｅ２であること、および、その構造がカルコパイライト型構造であることが確認できる。 The obtained sample is identified using, for example, X-ray diffraction (XRD). For example, when Cu 2 Te and Ga 2 Te 3 are melted at a ratio of 1: 1, it is confirmed from XRD that the obtained bulk body is CuGaTe 2 and the structure thereof is a chalcopyrite structure. I can confirm.

図２に、ＣｕＧａＴｅ化合物のＸ線回折の結果を示す。図２では、Ｃｕ２ＴｅおよびＧａ２Ｔｅ３を１：１の割合で溶解させたものをＣＧＴ−１１２と示しており、Ｃｕ２ＴｅおよびＧａ２Ｔｅ３を３：５の割合で溶解させたものをＣＧＴ−３５９と示している。同様に、Ｃｕ２ＴｅおよびＧａ２Ｔｅ３を１：３の割合で溶解させたものをＣＧＴ−１３５と示しており、Ｃｕ２ＴｅおよびＧａ２Ｔｅ３を１：５の割合で溶解させたものをＣＧＴ−１５８と示している。図２に示したＸ線回折の結果は、ＣＧＴ−１１２、ＣＧＴ−３５９、ＣＧＴ−１３５、ＣＧＴ−１５８は、それぞれ、ＣｕＧａＴｅ２、Ｃｕ３Ｇａ５Ｔｅ９、ＣｕＧａ３Ｔｅ５およびＣｕＧａ５Ｔｅ８の結晶と同様の結果を示しており、これにより、所定の割合で溶解したＣｕＧａＴｅ化合物が得られたことがわかる。 FIG. 2 shows the results of X-ray diffraction of the CuGaTe compound. In FIG. 2, the Cu 2 Te and Ga 2 Te 3 1: those dissolved at a ratio of 1 shows the CGT-112, a Cu 2 Te and Ga 2 Te 3 3: dissolved at a rate of 5 This is shown as CGT-359. Similarly, a solution in which Cu 2 Te and Ga 2 Te 3 are dissolved in a ratio of 1: 3 is shown as CGT-135, and Cu 2 Te and Ga 2 Te 3 are dissolved in a ratio of 1: 5. Is shown as CGT-158. Results of X-ray diffraction shown in FIG. 2, CGT-112, CGT- 359, CGT-135, CGT-158 , respectively, CuGaTe 2, Cu 3 Ga 5 Te 9, CuGa 3 Te 5 and CuGa 5 Te 8 This shows the same result as that of the crystal, and it can be seen that a CuGaTe compound dissolved at a predetermined ratio was obtained.

ここで、ＣｕＧａＴｅ２、Ｃｕ３Ｇａ５Ｔｅ９、ＣｕＧａ３Ｔｅ５およびＣｕＧａ５Ｔｅ８の結晶構造を検討する。ＣｕＧａＴｅ化合物では、カチオンサイトおよびアニオンサイトの割合は１：１であり、カチオンサイトにＣｕおよびＧａが占有し、アニオンサイトにＴｅが占有する。これらのＣｕＧａＴｅ化合物のうちのいくつかではＣｕおよびＧａの原子数の和とＴｅの原子数とが一致しておらず、カチオンサイトに空孔が存在している。ＣｕＧａＴｅ２、Ｃｕ３Ｇａ５Ｔｅ９、ＣｕＧａ３Ｔｅ５およびＣｕＧａ５Ｔｅ８の空孔の割合は、それぞれ０、１/１８、１/１０、１/８である。 Here, the crystal structures of CuGaTe 2 , Cu 3 Ga 5 Te 9 , CuGa 3 Te 5 and CuGa 5 Te 8 will be examined. In the CuGaTe compound, the ratio of the cation site and the anion site is 1: 1, Cu and Ga occupy the cation site, and Te occupy the anion site. In some of these CuGaTe compounds, the sum of the number of Cu and Ga atoms does not match the number of Te atoms, and vacancies exist in the cation site. The ratios of the holes of CuGaTe 2 , Cu 3 Ga 5 Te 9 , CuGa 3 Te 5 and CuGa 5 Te 8 are 0, 1/18, 1/10 and 1/8, respectively.

以下、図３〜図６を参照して、ＣｕＧａＴｅ化合物の空孔の割合と、特性の温度依存性を説明する。図３に、ＣｕＧａＴｅ化合物の電気抵抗率の温度依存性を示す。図３から理解されるように、ＣｕＧａＴｅ化合物のいずれにおいても電気抵抗率は温度の増加とともに減少する。一般に、温度が増加すると、キャリアの移動度が減少するが、キャリアの数が増大する影響が大きいため、抵抗率が減少する。また、特に６００Ｋ以上の所定の温度に着目すると、電気抵抗率は、空孔の割合が高いほど高い傾向がある。これは、空孔が、キャリアの散乱に寄与しているためと考えられる。   Hereinafter, with reference to FIG. 3 to FIG. 6, the ratio of vacancies in the CuGaTe compound and the temperature dependence of the characteristics will be described. FIG. 3 shows the temperature dependence of the electrical resistivity of the CuGaTe compound. As can be seen from FIG. 3, the electrical resistivity decreases with increasing temperature in any of the CuGaTe compounds. In general, as the temperature increases, the mobility of carriers decreases, but the resistivity decreases because the effect of increasing the number of carriers is large. In particular, when attention is paid to a predetermined temperature of 600 K or higher, the electrical resistivity tends to be higher as the ratio of holes is higher. This is presumably because the vacancies contribute to carrier scattering.

図４に、ＣｕＧａＴｅ化合物のゼーベック係数の温度依存性を示す。特に７００Ｋ未満の比較的低い温度において、ＣｕＧａＴｅ２、ＣｕＧａ３Ｔｅ５、ＣｕＧａ５Ｔｅ８のゼーベック係数は比較的高いのに対して、Ｃｕ３Ｇａ５Ｔｅ８のゼーベック係数は比較的低い。一方、温度が比較的高くなると、異なるＣｕＧａＴｅ化合物におけるゼーベック係数の差が小さくなる。 FIG. 4 shows the temperature dependence of the Seebeck coefficient of the CuGaTe compound. Particularly at a relatively low temperature of less than 700 K, the Seebeck coefficient of CuGaTe 2 , CuGa 3 Te 5 , and CuGa 5 Te 8 is relatively high, whereas the Seebeck coefficient of Cu 3 Ga 5 Te 8 is relatively low. On the other hand, when the temperature is relatively high, the difference in Seebeck coefficient between different CuGaTe compounds becomes small.

図５に、ＣｕＧａＴｅ化合物の熱伝導率の温度依存性を示す。ＣｕＧａＴｅ化合物のいずれにおいても熱伝導率は温度の増加とともに減少する。これは、温度の増加により、フォノンによる熱伝達の散乱が激しくなるからと考えられる。また、同一温度で比較した場合、空孔の割合が高いほど熱電導率は低い。これは、空孔が、フォノンによる熱伝達を散乱しているためと考えられる。このように、空孔はキャリアだけでなくフォノンによる熱伝達も散乱する。なお、空孔が少ないほど、温度変化に応じた熱伝導率の変化率が大きく、ＣｕＧａＴｅ２の熱伝導率は低温時に比較的高いが、温度の増加とともに大きく減少する。 FIG. 5 shows the temperature dependence of the thermal conductivity of the CuGaTe compound. In any CuGaTe compound, the thermal conductivity decreases with increasing temperature. This is presumably because the scattering of heat transfer due to phonons increases with an increase in temperature. Further, when compared at the same temperature, the higher the percentage of holes, the lower the thermal conductivity. This is presumably because the vacancies scatter heat transfer by phonons. In this way, the holes scatter not only carriers but also heat transfer by phonons. Note that the smaller the number of holes, the greater the rate of change of thermal conductivity in accordance with the temperature change, and the thermal conductivity of CuGaTe 2 is relatively high at low temperatures, but greatly decreases with increasing temperature.

図６に、ＣｕＧａＴｅ化合物の性能指数の温度依存性を示す。温度が同じ場合、空孔の割合が低いほど性能指数は高い。特に、ＣｕＧａＴｅ２の性能指数は温度の増加とともに大きく増加する。これは、温度の増加とともにＣｕＧａＴｅ２の熱伝導率が大きく減少していることが寄与していると考えられる。例えば、温度が９５０℃の場合、ＣｕＧａＴｅ２の指数ＺＴは１．６６である。 FIG. 6 shows the temperature dependence of the figure of merit of the CuGaTe compound. If the temperature is the same, the lower the percentage of holes, the higher the figure of merit. In particular, the figure of merit of CuGaTe 2 increases greatly with increasing temperature. This is thought to be due to the fact that the thermal conductivity of CuGaTe 2 greatly decreases with increasing temperature. For example, when the temperature is 950 ° C., the index ZT of CuGaTe 2 is 1.66.

本発明によれば、新規な材料で比較的簡便に作製可能な熱電変換素子が提供される。特に、熱電変換材料がＣｕＧａＴｅ２である場合、高い性能指数を実現することができる。このような熱電変換素子は、例えば、発電所におけるコジェネレーションシステムや自動車の発電システムに好適に用いられる。または、熱電変換素子はプロジェクタに取り付けられ、プロジェクタから発生した熱を利用して発電を行ってもよい。あるいは、熱電変換素子は地熱を利用して発電を行ってもよい。 ADVANTAGE OF THE INVENTION According to this invention, the thermoelectric conversion element which can be produced comparatively simply with a novel material is provided. In particular, when the thermoelectric conversion material is CuGaTe 2 , a high figure of merit can be realized. Such a thermoelectric conversion element is suitably used for, for example, a cogeneration system in a power plant or a power generation system of an automobile. Alternatively, the thermoelectric conversion element may be attached to the projector and generate power using heat generated from the projector. Alternatively, the thermoelectric conversion element may generate power using geothermal heat.

１０ 熱電変換素子
２０ｐ ｐ型半導体層
２０ｎ ｎ型半導体層
２２ 電極
２４ａ 電極
２４ｂ 電極 10 thermoelectric conversion element 20p p-type semiconductor layer 20n n-type semiconductor layer 22 electrode 24a electrode 24b electrode

Claims (8)

ｎ型半導体層と、
ｐ型半導体層と
を備える、熱電変換素子であって、
前記ｐ型半導体層は、ＣｕＧａＴｅ２、Ｃｕ３Ｇａ５Ｔｅ９、ＣｕＧａ３Ｔｅ５およびＣｕＧａ５Ｔｅ８からなる群から選択された少なくとも１つを含む、熱電変換素子。 an n-type semiconductor layer;
a thermoelectric conversion element comprising a p-type semiconductor layer,
The p-type semiconductor layer is a thermoelectric conversion element including at least one selected from the group consisting of CuGaTe 2 , Cu 3 Ga 5 Te 9 , CuGa 3 Te 5 and CuGa 5 Te 8 . ８００Ｋ以上の温度下で用いられる、請求項１に記載の熱電変換素子。   The thermoelectric conversion element according to claim 1, which is used at a temperature of 800K or higher. 前記ｐ型半導体層は、ＣｕＧａＴｅ２を含む、請求項１または２に記載の熱電変換素子。 The thermoelectric conversion element according to claim 1, wherein the p-type semiconductor layer includes CuGaTe 2 . 前記ｐ型半導体層と前記ｎ型半導体層のそれぞれと接触する電極をさらに備える、請求項１から３のいずれかに記載の熱電変換素子。   The thermoelectric conversion element according to any one of claims 1 to 3, further comprising an electrode in contact with each of the p-type semiconductor layer and the n-type semiconductor layer. ＣｕＧａＴｅ２、Ｃｕ３Ｇａ５Ｔｅ９、ＣｕＧａ３Ｔｅ５およびＣｕＧａ５Ｔｅ８からなる群から選択された少なくとも１つを含む熱電変換材料。 A thermoelectric conversion material containing at least one selected from the group consisting of CuGaTe 2 , Cu 3 Ga 5 Te 9 , CuGa 3 Te 5 and CuGa 5 Te 8 . ｎ型半導体層を用意する工程と、
ｐ型半導体層を用意する工程と、
前記ｎ型半導体層および前記ｐ型半導体層を電気的に接続する工程と
を包含し、
前記ｐ型半導体層を用意する工程において、前記ｐ型半導体層はＣｕＧａＴｅ２、Ｃｕ３Ｇａ５Ｔｅ９、ＣｕＧａ３Ｔｅ５およびＣｕＧａ５Ｔｅ８からなる群から選択された少なくとも１つを含む、熱電変換素子の作製方法。 preparing an n-type semiconductor layer;
preparing a p-type semiconductor layer;
Electrically connecting the n-type semiconductor layer and the p-type semiconductor layer,
In the step of preparing the p-type semiconductor layer, the p-type semiconductor layer includes at least one selected from the group consisting of CuGaTe 2 , Cu 3 Ga 5 Te 9 , CuGa 3 Te 5 and CuGa 5 Te 8. A method for manufacturing a conversion element. 前記ｐ型半導体層を用意する工程は、化学量論的に所定の割合でＣｕ、ＧａおよびＴｅの存在する原料を用意し、上記原料の溶融を行う工程を含む、請求項６に記載の熱電変換素子の作製方法。   The step of preparing the p-type semiconductor layer includes a step of preparing a raw material containing Cu, Ga and Te in a stoichiometric predetermined ratio and melting the raw material. A method for manufacturing a conversion element. 前記ｐ型半導体層を用意する工程において、前記ｐ型半導体層はＣｕＧａＴｅ２を含む、請求項６または７に記載の熱電変換素子の作製方法。 The method for producing a thermoelectric conversion element according to claim 6, wherein in the step of preparing the p-type semiconductor layer, the p-type semiconductor layer contains CuGaTe 2 .
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