JPWO2015125823A1 - Semiconductor single crystal and power generation method using the same - Google Patents

Abstract

A semiconductor having an n-type semiconductor portion 12, a p-type semiconductor portion 14, and an intrinsic semiconductor portion 16 therebetween, and the intrinsic semiconductor portion 16 has a smaller band gap than the n-type semiconductor portion 12 and the p-type semiconductor portion 14. A single crystal 10 is provided.

Description

  The present disclosure relates to a semiconductor single crystal and a power generation method using the same.

  Internal combustion engines such as automobiles and aircraft use energy obtained by burning fossil fuels. At present, the energy efficiency of the internal combustion engine is only about 30%, and most is released as thermal energy. In order to effectively use this thermal energy, various thermoelectric materials utilizing the Seebeck effect have been studied.

Various semiconductor materials have been studied as thermoelectric materials. For example, Patent Literature 1 discloses a thermoelectric element having CoSb ₃ as a p-type semiconductor thermoelectric material and CoSb ₂ as an n-type semiconductor thermoelectric material. Patent Document 2 proposes a thermoelectric element that is a sintered body of a Si clathrate compound. A dimensionless figure of merit ZT value is presented as one of the indexes for evaluating the performance of such thermoelectric elements. In order to improve the ZT value, various methods have been studied.

  The clathrate compound is composed of eight cage networks composed of Group IV elements such as Si, and Group I or Group II atoms (guest atoms) encapsulated one by one in the cage. Since the guest atoms vibrate at a low frequency and phonons are scattered, the clathrate compound has a sufficiently low thermal conductivity. Such low thermal conductivity contributes to the improvement of the ZT value.

  As described above, the clathrate compound has a sufficiently low thermal conductivity. Another approach to improve the figure of merit ZT value is to reduce the resistivity. Here, in general, since a polycrystalline body such as a sintered body includes many grain boundaries, the specific resistance tends to increase. For this reason, Patent Document 3 proposes to increase the figure of merit ZT by using a clathrate compound as a single crystal.

JP 2009-105101 A JP 2006-57124 A JP 2004-67425 A

  Although various methods for improving the ZT value of the thermoelectric material have been studied in this way, the thermoelectric conversion efficiency still has room for improvement. Thermoelectric materials generate power using the difference in electromotive force based on the temperature difference. When a power generation module is assembled using thermoelectric materials, the temperature difference decreases due to heat conduction, etc. There is a concern that it will decrease. For this reason, a cooling device or the like for maintaining the temperature difference is required, and the module becomes complicated.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a semiconductor single crystal that can generate power even if there is no temperature difference between the semiconductor portions. Another object of the present invention is to provide a power generation method capable of generating power efficiently by using such a semiconductor single crystal.

  In order to solve the above-described problems, the present inventors have studied various materials that can generate power even if there is no temperature difference between the semiconductor portions. As a result, it has been found that power can be generated even if there is no temperature difference by controlling the band gap of the semiconductor single crystal.

  In one aspect, the present invention includes an n-type semiconductor portion, a p-type semiconductor portion, and an intrinsic semiconductor portion between them, and the intrinsic semiconductor portion has a smaller band gap than the n-type semiconductor portion and the p-type semiconductor portion. A semiconductor single crystal is provided.

  When the semiconductor single crystal is heated to a predetermined temperature range, even if there is no temperature difference between the n-type semiconductor portion and the p-type semiconductor portion, only in the intrinsic semiconductor portion at the pn junction portion, the conduction band from the valence band. Electrons are excited on the surface. The electrons excited in the conduction band move to the n-type semiconductor portion having low energy, and the holes generated in the valence band move to the p-type semiconductor portion. Due to the bias of the carriers caused by these movements, a power generation material is obtained in which the p-type semiconductor portion side is a positive electrode and the n-type semiconductor portion side is a negative electrode. By heating the semiconductor single crystal to a predetermined temperature range in this way, it is possible to generate power in the predetermined temperature range even if there is no temperature difference between the n-type semiconductor portion and the p-type semiconductor portion.

In the semiconductor single crystal according to some embodiments of the present invention, the concentration of at least one of the elements constituting the single crystal may be higher in the order of the p-type semiconductor portion, the intrinsic semiconductor portion, and the n-type semiconductor portion. Good. The semiconductor single crystal may contain a clathrate compound represented by the following formula (I). The semiconductor single crystal may be a clathrate compound represented by the following formula (I).
_{A x B y C 46-y} (I)

  In formula (I), A represents at least one element selected from the group consisting of Ba, Na, Sr and K, and B represents at least one element selected from the group consisting of Au, Ag, Cu, Ni and Al. Represents an element, and C represents at least one element selected from the group consisting of Si, Ge and Sn. x is 7 to 8, y is 3.5 to 6 or 11 to 17, and y / x is higher in the order of the p-type semiconductor part, the intrinsic semiconductor part, and the n-type semiconductor part.

The semiconductor single crystal may contain a clathrate compound represented by the following formula (II). The semiconductor single crystal may be a clathrate compound represented by the following formula (II).
Ba _x Au _y Si _46-y (II)
In formula (II), x is 7 to 8, y is 3.5 to 6, and y / x is higher in the order of the p-type semiconductor portion, the intrinsic semiconductor portion, and the n-type semiconductor portion.

  By making the compound constituting the semiconductor single crystal a clathrate compound represented by the formula (I) or the formula (II), the potential difference between the n-type semiconductor portion and the p-type semiconductor portion is further increased. Can do. As a result, the power generation amount can be further increased.

  In another aspect, the present invention includes a first semiconductor portion made of an n-type semiconductor portion or a p-type semiconductor portion, and a semiconductor having different band gaps at one end and the other end of the first semiconductor portion. A single crystal is provided.

  When the semiconductor single crystal is heated to a predetermined temperature range, even if there is no temperature difference between one end portion and the other end portion of the first semiconductor portion, the valence electrons are only in one of both end portions. Electrons can be excited from the band to the conduction band. For example, an electron excited in the conduction band at one end moves to the other end having low energy. Alternatively, a hole generated in the charged band moves to the other end portion having high energy. Due to the bias of the carrier caused by any of these movements, a power generation material in which one of both ends is a positive electrode and the other is a negative electrode. By heating the semiconductor single crystal to a predetermined temperature range in this way, it is possible to generate power within the predetermined temperature range even if there is no temperature difference between both ends.

  The semiconductor single crystal may contain a clathrate compound represented by the formula (I). In the above formula (I), A represents at least one element selected from the group consisting of Ba, Na, Sr and K, and B is selected from the group consisting of Au, Ag, Cu, Ni and Al. It represents at least one element, and C represents at least one element selected from the group consisting of Si, Ge, and Sn. When the first semiconductor portion is an n-type semiconductor portion, x is 7 to 8, and y is 3.5 to 5.5 or 11 to 16. When the first semiconductor portion is a p-type semiconductor portion, x is 7 to 8, and y is 5.3 to 6 or 16 to 17. y / x is different at one end and the other end. The semiconductor single crystal may contain a clathrate compound represented by the formula (II). At this time, x, y, and y / x in the formula (II) are as described above.

  The semiconductor single crystal has a second semiconductor portion made of an intrinsic semiconductor portion so as to be adjacent to the first semiconductor portion, and the second semiconductor portion has a smaller band gap than the first semiconductor portion. It may be.

  When the semiconductor single crystal is heated to a predetermined temperature range, electrons are transferred from the valence band to the conduction band only in the intrinsic semiconductor portion, even if there is no temperature difference between the first semiconductor portion and the second semiconductor portion. Excited. When the first semiconductor part is an n-type semiconductor part, the electrons excited in the conduction band move to the n-type semiconductor part having low energy. Due to the bias of the carrier caused by this movement, a power generation material having the intrinsic semiconductor portion side as the positive electrode and the n-type semiconductor portion side as the negative electrode is obtained. On the other hand, when the first semiconductor portion is a p-type semiconductor portion, holes generated in the charge band in the second semiconductor portion move to the p-type semiconductor portion. Due to the deviation of the carriers caused by this movement, a power generation material is obtained in which the p-type semiconductor portion side is a positive electrode and the genuine semiconductor portion side is a negative electrode. By heating the semiconductor single crystal to a predetermined temperature range in this way, power can be generated within the predetermined temperature range even if there is no temperature difference between the first semiconductor portion and the second semiconductor portion. it can.

  The first semiconductor portion and the second semiconductor portion in the semiconductor single crystal may contain a clathrate compound represented by the above formula (I). However, when the 1st semiconductor part consists of an n-type semiconductor part, x is 7-8 and y is 3.5-5.5 or 11-16. When the first semiconductor portion is an n-type semiconductor portion, x is 7 to 8, y is 3.5 to 5.5, or 11 to 16, and y / x is the n-type semiconductor portion of the intrinsic semiconductor portion. Higher than. When the first semiconductor portion is a p-type semiconductor portion, x is 7 to 8, y is 5.3 to 6 or 16 to 17, and y / x is the p-type semiconductor portion than the intrinsic semiconductor portion. high.

  The first semiconductor portion and the second semiconductor portion in the semiconductor single crystal may include a clathrate compound represented by the above formula (II). In Formula (II), when a 1st semiconductor part consists of an n-type semiconductor part, x is 7-8 and y is 3.5-5.5 or 11-16. When the second semiconductor portion is included, y / x is higher in the intrinsic semiconductor portion than in the n-type semiconductor portion. When the first semiconductor portion is a p-type semiconductor portion, x is 7 to 8, and y is 5.3 to 6 or 16 to 17. When the second semiconductor portion is included, y / x is higher in the p-type semiconductor portion than in the intrinsic semiconductor portion.

  In some embodiments of the present invention, the semiconductor single crystal can have an absolute value of a potential difference between both ends at 400 ° C. of 0.3 mV or more.

In still another aspect, the present invention provides a semiconductor single crystal having an n-type semiconductor portion, a p-type semiconductor portion, and an intrinsic semiconductor portion therebetween, and includes a clathrate compound represented by the following formula (I): A semiconductor single crystal is provided. The semiconductor single crystal may be a clathrate compound represented by the following formula (I).
_{A x B y C 46-y} (I)

  In formula (I), A represents at least one element selected from the group consisting of Ba, Na, Sr and K, and B represents at least one element selected from the group consisting of Au, Ag, Cu, Ni and Al. Represents an element, and C represents at least one element selected from the group consisting of Si, Ge and Sn. x is 7 to 8, y is a value of 3.5 to 6 or 11 to 17, and y / x is higher in the order of the p-type semiconductor part, the intrinsic semiconductor part, and the n-type semiconductor part.

  That is, the semiconductor single crystal has a composition in which y / x is higher in the order of the p-type semiconductor portion, the intrinsic semiconductor portion, and the n-type semiconductor portion. Such a semiconductor single crystal can generate power in a predetermined temperature range even if there is no temperature difference between the p-type semiconductor portion and the n-type semiconductor portion.

  Although the reason for this is not necessarily clear, the present inventors are due to the fact that the band gap of the intrinsic semiconductor portion at the pn junction is smaller than the band gap of the p-type semiconductor portion and the n-type semiconductor portion. I think there is. That is, when the semiconductor single crystal of the present invention is heated to a predetermined temperature range, a pn junction portion having a small band gap even if there is no temperature difference between the n-type semiconductor portion and the p-type semiconductor portion within the predetermined temperature range. Only in the intrinsic semiconductor part, electrons are easily excited from the valence band to the conduction band.

  Electrons excited to the conduction band in the intrinsic semiconductor portion move to the n-type semiconductor portion having low energy. On the other hand, holes generated in the valence band in the intrinsic semiconductor portion move to the p-type semiconductor portion. Due to the bias of carriers generated by these movements, the semiconductor single crystal becomes a power generation material with the p-type semiconductor side as the positive electrode and the n-type semiconductor side as the negative electrode. With such a mechanism, it is considered that the semiconductor single crystal can generate power in a predetermined temperature range even if there is no temperature difference between the p-type semiconductor portion and the n-type semiconductor portion.

  In still another aspect, the present invention provides a semiconductor single crystal having a first semiconductor part composed of an n-type semiconductor part or a p-type semiconductor part and containing a clathrate compound represented by the above formula (I).

  In Formula (I), when a 1st semiconductor part consists of an n-type semiconductor, x is 7-8 and y is 3.5-5.5 or 11-16. When the first semiconductor portion is made of a p-type semiconductor, x is 7 to 8, and y is 5.3 to 6 or 16 to 17. y / x is different between one end and the other end of the semiconductor single crystal.

  The semiconductor single crystal can generate power in a predetermined temperature range even if there is no temperature difference between one end and the other end. One reason for this is considered to be that the band gap at one end is smaller or larger than the band gap at the other end. That is, when the semiconductor single crystal is heated to a predetermined temperature range, even if there is no temperature difference between one end portion and the other end portion, only the end portion with the smaller bandgap is from the valence band. Electrons are easily excited in the conduction band.

  At one end, either the electrons excited in the conduction band or the holes generated in the valence band move to the other end. This creates a potential difference between the ends. By such a mechanism, it is considered that the semiconductor single crystal can generate power in a predetermined temperature range even if there is no temperature difference between the end portions.

  The semiconductor single crystal has a second semiconductor portion made of an intrinsic semiconductor portion so as to be adjacent to the first semiconductor portion, and the intrinsic semiconductor portion contains a clathrate compound represented by the above formula (I). Also good. When the first semiconductor portion is an n-type semiconductor portion, y / x is higher in the intrinsic semiconductor portion than in the n-type semiconductor portion. When the first semiconductor part is a p-type semiconductor part, y / x is higher in the p-type semiconductor part than in the intrinsic semiconductor part.

  The semiconductor single crystal can generate power in a predetermined temperature range even if there is no temperature difference between the first semiconductor portion and the second semiconductor portion. The reason for this is not necessarily clear, but the present inventors believe that one reason is that the band gap of the second semiconductor portion is smaller than the band gap of the first semiconductor portion. That is, when the semiconductor single crystal is heated to a predetermined temperature range, even if there is no temperature difference between the first semiconductor portion and the second semiconductor portion, the second crystal composed of an intrinsic semiconductor portion having a small band gap. Only in the semiconductor part, electrons are easily excited from the valence band to the conduction band.

  When the first semiconductor portion is an n-type semiconductor portion, the electrons excited to the conduction band in the second semiconductor portion made of the intrinsic semiconductor portion move to the n-type semiconductor portion having low energy. The semiconductor single crystal becomes a power generation material with the intrinsic semiconductor portion side as the positive electrode and the n-type semiconductor side as the negative electrode due to the carrier deviation caused by this movement. On the other hand, when the first semiconductor portion is a p-type semiconductor portion, holes generated in the valence band in the second semiconductor portion made of the intrinsic semiconductor portion move to the p-type semiconductor portion. With such a mechanism, it is considered that the semiconductor single crystal can generate power in a predetermined temperature range even if there is no temperature difference between the first semiconductor portion and the second semiconductor portion.

In some embodiments of the present invention, the clathrate compound may be a compound represented by formula (II). In formula (II), x is 7-8 and y is 3.5-6.
Ba _x Au _y Si _46-y (II)

  By making the compound constituting the semiconductor single crystal a clathrate compound represented by the formula (II), the potential difference between the n-type semiconductor portion and the p-type semiconductor portion can be further increased. As a result, the power generation amount can be further increased. In some embodiments of the present invention, the semiconductor single crystal can have an absolute value of a potential difference between both ends at 400 ° C. of 0.3 mV or more.

  In still another aspect, the present invention provides a power generation method for generating power by heating the semiconductor single crystal described above. In this power generation method, since the semiconductor single crystal having the above-described characteristics is used, even if there is no temperature difference, it is possible to efficiently generate power within a predetermined temperature range.

  ADVANTAGE OF THE INVENTION According to this invention, even if there is no temperature difference between each semiconductor part, the semiconductor single crystal which can generate electric power can be provided. In addition, by using such a semiconductor single crystal, it is possible to provide a power generation method capable of generating power efficiently.

FIG. 1 is a diagram schematically showing a configuration of a semiconductor single crystal according to an embodiment of the present invention. FIG. 2A is a conceptual diagram showing a state of thermal excitation when the semiconductor single crystal according to one embodiment of the present invention is heated to a predetermined temperature. FIG. 2B is a conceptual diagram showing movement of electrons and holes when the semiconductor single crystal according to one embodiment of the present invention is heated to a predetermined temperature. FIG. 3A is a diagram showing band energy when y = 4 in a clathrate compound of Ba ₈ Au _y Si _46-y . FIG. 3B is a diagram showing band energy when y = 5 in a clathrate compound of Ba ₈ Au _y Si _46-y . FIG. 3C is a diagram showing band energy when y = 6 in the clathrate compound of Ba ₈ Au _y Si _46-y . FIG. 4A is a diagram showing band energy when y = 14 in a clathrate compound of Ba ₈ Al _y Si _46-y . FIG. 4B is a diagram showing band energy when y = 15 in the clathrate compound of Ba ₈ Al _y Si _46-y . FIG. 4C is a diagram showing band energy when y = 16 in the clathrate compound of Ba ₈ Al _y Si _46-y . FIG. 5A is a diagram showing band energy when y = 4 in a clathrate compound of Ba ₈ Cu _y Si _46-y . FIG. 5B is a diagram showing band energy in the case of y5 in a clathrate compound of Ba ₈ Cu _y Si _46-y . FIG. 5C is a diagram showing band energy when y = 6 in the clathrate compound of Ba ₈ Cu _y Si _46-y . FIG. 6 is a diagram schematically showing a configuration of a semiconductor single crystal according to another embodiment of the present invention. FIG. 7A is a conceptual diagram showing a state of thermal excitation when a semiconductor single crystal according to another embodiment of the present invention is heated to a predetermined temperature. FIG. 7B is a conceptual diagram showing the movement of electrons when a semiconductor single crystal according to another embodiment of the present invention is heated to a predetermined temperature. FIG. 8 is a diagram schematically showing a configuration of a semiconductor single crystal according to still another embodiment of the present invention. FIG. 9A is a conceptual diagram showing a state of thermal excitation when a semiconductor single crystal according to still another embodiment of the present invention is heated to a predetermined temperature. FIG. 9B is a conceptual diagram showing movement of holes when a semiconductor single crystal according to still another embodiment of the present invention is heated to a predetermined temperature. FIG. 10 is a diagram schematically showing a configuration of a semiconductor single crystal according to still another embodiment of the present invention. FIG. 11A is a conceptual diagram showing a state of thermal excitation when a semiconductor single crystal according to still another embodiment of the present invention is heated to a predetermined temperature. FIG. 11B is a conceptual diagram showing electron movement when a semiconductor single crystal according to still another embodiment of the present invention is heated to a predetermined temperature. FIG. 12A is a conceptual diagram showing a state of thermal excitation when a semiconductor single crystal according to still another embodiment of the present invention is heated to a predetermined temperature. FIG. 12B is a conceptual diagram showing electron movement when a semiconductor single crystal according to still another embodiment of the present invention is heated to a predetermined temperature. FIG. 13 is an optical micrograph of the semiconductor single crystal of Example 1. FIG. 14A is a diagram showing a measurement result of X-ray diffraction of the semiconductor single crystal of Example 1. FIG. FIG. 14B is a diagram showing a simulation result of X-ray diffraction. FIG. 15 is a graph showing the measurement results of the Seebeck coefficient of a sample obtained by cutting the semiconductor single crystal of Example 1. FIG. 16 is a graph showing a measurement result of electromotive force of a sample obtained by cutting the semiconductor single crystal of Example 1. FIG. 17 is a graph showing measurement results of electromotive force of a sample obtained by cutting the semiconductor single crystal of Example 1. FIG. 18 is an optical micrograph of the semiconductor single crystal of Example 2. FIG. 19A is a diagram illustrating a measurement result of X-ray diffraction of the semiconductor single crystal of Example 2, and FIG. 19B is a diagram illustrating a simulation result of X-ray diffraction. FIG. 20 is a graph showing the measurement results of the Seebeck coefficient of a sample obtained by cutting the semiconductor single crystal of Example 2. FIG. 21 is a graph showing the measurement results of the Seebeck coefficient of a sample obtained by cutting the semiconductor single crystal of Example 2. FIG. 22 is a graph showing measurement results of electromotive force of a sample obtained by cutting the semiconductor single crystal of Example 2. FIG. 23 is an optical micrograph of the semiconductor single crystal of Example 3. FIG. 24 is a graph showing measurement results of Seebeck coefficient of a sample obtained by cutting the semiconductor single crystal of Example 3. FIG. 25 is a schematic diagram showing a method for measuring an electromotive force of a sample obtained by cutting the semiconductor single crystal of Example 3. FIG. 26 is a graph showing measurement results of electromotive force of a sample obtained by cutting the semiconductor single crystal of Example 3. FIG. 27 is an optical micrograph of the semiconductor single crystal of Example 4. FIG. 28 is a graph showing the measurement results of Seebeck coefficient of a sample obtained by cutting the semiconductor single crystal of Example 4. FIG. 29 is a graph showing measurement results of electromotive force of a sample obtained by cutting the semiconductor single crystal of Example 4.

  Preferred embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the following embodiments. In the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant descriptions are omitted in some cases.

  FIG. 1 is a diagram schematically showing the configuration of the semiconductor single crystal of the present embodiment. The shape of the semiconductor single crystal is not particularly limited, and may be, for example, a columnar shape. As shown in FIG. 1, when the semiconductor single crystal 10 is columnar or plate-shaped, the semiconductor single crystal 10 has an n-type semiconductor portion 12 on the upper side and a p-type semiconductor portion 14 on the lower side. be able to. The semiconductor single crystal 10 has an intrinsic semiconductor portion 16 at a pn junction between the n-type semiconductor portion 12 and the p-type semiconductor portion 14.

  In such a semiconductor single crystal 10, the concentration of a predetermined element changes from the n-type semiconductor portion 12 toward the p-type semiconductor portion 14. Such a concentration gradient of elements contributes to the band gap distribution of the semiconductor single crystal 10 as described below.

  2A and 2B are conceptual diagrams showing the band gap state of the semiconductor single crystal of the present embodiment. 2A and 2B, the vertical axis represents the energy of electrons, and the horizontal axis represents the distance from the end of the semiconductor single crystal on the n-type semiconductor portion 12 side. As shown in FIGS. 2A and 2B, the band gap in the intrinsic semiconductor portion 16 is smaller than the band gap in the n-type semiconductor portion 12 and the p-type semiconductor portion 14. The n-type semiconductor part 12 is a part where the Fermi level f is on the conduction band side, and the p-type semiconductor part 14 is a part where the Fermi level f is on the valence band side. The intrinsic semiconductor portion 16 is a portion where the Fermi level f is at the center of the forbidden band between the conduction band and the valence band.

  FIG. 2A is a conceptual diagram showing a state of thermal excitation when the semiconductor single crystal 10 is heated to a predetermined temperature. As shown in FIG. 2A, when the semiconductor single crystal 10 is heated to a predetermined temperature, electrons in the valence band are thermally excited to the conduction band. At this time, electrons are thermally excited in the conduction band only by the intrinsic semiconductor portion 16 of the pn junction having a relatively small band gap. On the other hand, electrons are not thermally excited in the p-type semiconductor unit 14 and the n-type semiconductor unit 12 whose band gap is larger than that of the intrinsic semiconductor unit 16.

  FIG. 2B is a conceptual diagram showing movement of electrons (black circles) and holes (white circles) when the semiconductor single crystal 10 is heated to a predetermined temperature. As shown in FIG. 2B, the electrons excited in the conduction band move to the lower energy side, that is, the n-type semiconductor portion 12 side. On the other hand, holes generated on the valence band side due to excitation of electrons move to the p-type semiconductor portion 14 side having low energy. As a result, the n-type semiconductor portion 12 is negatively charged and the p-type semiconductor portion 14 is positively charged, so that an electromotive force is generated. In this way, the semiconductor single crystal 10 can generate power even if there is no temperature difference between the n-type semiconductor portion 12 and the p-type semiconductor portion 14. Such an electromotive force generation mechanism is different from the Seebeck effect that generates an electromotive force based on a temperature difference.

  Since the semiconductor single crystal 10 of the present embodiment can generate power even if there is no temperature difference, equipment for temperature control such as cooling or heating can be eliminated or simplified even when modularized. Therefore, the semiconductor single crystal 10 can be suitably used as a power generation material for thermoelectric conversion or exhaust heat recovery. For example, as a power generation module, it can be installed in transportation equipment, devices such as automobiles and airplanes having an internal combustion engine, plants, and the like.

  The ratio of the band gap width (energy gap) of the intrinsic semiconductor portion 16 to the band gap width (energy gap) in the n-type semiconductor portion 12 and the p-type semiconductor portion 14 is not particularly limited, but is preferably smaller. For example, the ratio may be 0.8 or less, or 0.1 to 0.7. The smaller this ratio, the wider the temperature range in which power can be generated.

  The energy gap of the intrinsic semiconductor part 16 may be 0.4 eV or less, for example, and may be 0.05 to 0.3 eV. The energy gap in the n-type semiconductor unit 12, the p-type semiconductor unit 14, and the intrinsic semiconductor unit 16 can be measured by, for example, inverse photoelectron spectroscopy.

The material constituting the semiconductor single crystal 10 may be a clathrate compound represented by the following formula (I) having A, B, and C as constituent elements.
_{A x B y C 46-y} (I)

  In formula (I), A represents at least one element selected from the group consisting of Ba, Na, Sr and K, and B represents at least one element selected from the group consisting of Au, Ag, Cu, Ni and Al. Represents an element, and C represents at least one element selected from the group consisting of Si, Ge and Sn. x is 7-8, and y is 3.5-6 or 11-17.

  In the clathrate compound, the A element functions as a monovalent or divalent donor, and the B element functions as a trivalent or monovalent acceptor. In the semiconductor single crystal 10, y indicating the molar ratio of the B element in the clathrate compound increases along the arrow α direction in FIG. On the other hand, x indicating the molar ratio of the A element may be distributed substantially uniformly in the semiconductor single crystal 10 or may decrease along the direction of the arrow α in FIG. That is, in the semiconductor single crystal 10, the value of y / x generally increases along the arrow α direction from the upper end to the lower end in FIG. Therefore, the lower portion has a higher molar ratio (y / x) of the B element to the A element. Thus, the upper portion becomes the n-type semiconductor portion 12 and the lower portion becomes the p-type semiconductor portion 14. Note that the value of y / x increases in the order of the n-type semiconductor unit 12, the intrinsic semiconductor unit 16, and the p-type semiconductor unit 14. That is, the value of y / x is the lowest in the n-type semiconductor portion 12 and the highest in the p-type semiconductor portion 14.

The clathrate compound (clathrate compound) is composed of a cage structure composed of B element and C element and an A element included therein. As a normal clathrate compound, one in which the cage structure is composed of only the C element is known (for example, Ba ₈ Si ₄₆ ). However, the production of such clathrate compounds requires very high pressure. On the other hand, the structure in which the 6c site of the C element (Si) is substituted with the B element can be synthesized by an arc melting method at normal pressure.

Preferred examples of clathrate _{compound, Ba x Au y Si 46-} y ( where, x is 7 to 8, y is _{3.5~6.), Ba x Al y} Si 46-y ( where , X is 7 to 8 and y is 11 to 17.), and Ba _x Cu _x Si _46-y (where x is 7 to 8 and y is 3.5 to 6). Is mentioned. The semiconductor single crystal 10 made of such a clathrate compound becomes a very good power generation material by providing a concentration gradient of Au, Al or Cu as B elements.

FIG. 3A is a diagram showing band energy when y = 4 in a clathrate compound of Ba ₈ Au _y Si _46-y . FIG. 3B is a diagram showing band energy when y = 5 in a clathrate compound of Ba ₈ Au _y Si _46-y . FIG. 3C is a diagram showing band energy when y = 6 in the clathrate compound of Ba ₈ Au _y Si _46-y .

FIG. 4A is a diagram showing band energy when y = 14 in a clathrate compound of Ba ₈ Al _y Si _46-y . FIG. 4B is a diagram showing band energy when y = 15 in the clathrate compound of Ba ₈ Al _y Si _46-y . FIG. 4C is a diagram showing band energy when y = 16 in the clathrate compound of Ba ₈ Al _y Si _46-y .

FIG. 5A is a diagram showing band energy when y = 4 in a clathrate compound of Ba ₈ Cu _y Si _46-y . FIG. 5B is a graph showing band energy when y = 5 in a clathrate compound of Ba ₈ Cu _y Si _46-y . FIG. 5C is a diagram showing band energy when y = 6 in the clathrate compound of Ba ₈ Cu _y Si _46-y .

  The band energies shown in (A), (B), and (C) in FIGS. 3, 4, and 5 are derived using the first principle calculation software Advance / PHASE. In the derivation, the density functional method was used from the viewpoint of calculation speed and calculation accuracy, and PBE-GGA was used as the exchange interaction potential. As a calculation method, a projector augmented wave (PAW) method was used. K-Point (k point) was 4 × 4 × 4 = 64 points, and cut off energy was 340 eV. Table 1 shows the band gap width (energy gap) obtained from FIG.

From the results shown in Table 1, in the case of a clathrate compound such as Ba ₈ Au _y Si _46-y , the band gap width is considerably smaller in the composition of y = 5 than in the composition of y = 4 and y = 6. You can see that That is, the width of the band gap of Ba ₈ Au _y Si _46-y largely depends on the molar ratio of Au. On the other _hand, if the clathrate compound such as _{Ba 8 Al y Si 46-y} , the composition of y = 15, the width of the band gap is slightly smaller than the composition of y = 14 and y = 16 I understand. That _is, the width of the band gap of the Ba ₈ Al _{y Si 46-y} depends on the molar ratio of Al, the dependence _is smaller than the molar ratio of Au in the _{Ba 8 Au y Si 46-y} .

_{Ba 8 Au y Si 46-y} ( provided that y = 4 to 6.) _{Is, Ba 8 Al y Si 46-} y ( provided that y = 14 to 16.) Than the width of the band gap The difference is big. Thus, the semiconductor single crystal 10 made of a material having a larger band gap width difference can generate an electromotive force in a wider temperature range. Therefore, it can be set as the power generation material with higher versatility. _{However, Ba 8 Al y Si 46-} y is also a promising power material which causes an electromotive force at a predetermined temperature range.

In the case of the clathrate compound of Ba ₈ Cu _y Si _46-y , it can be seen that the band gap width is considerably smaller in the composition of y = 6 than in the composition of y = 4 and y = 5. That is, the width of the band gap of Ba ₈ Cu _y Si _46-y largely depends on the molar ratio of Cu. Ba ₈ Cu _y Si _46-y (where y = 4 to 6) has a band gap width larger than that of Ba ₈ Al _y Si _46-y (where y = 14 to 16). The difference is big. Therefore, the semiconductor single crystal 10 made of Ba ₈ Cu _y Si _46-y can also generate an electromotive force in a wide temperature range. Therefore, it can be set as the power generation material with higher versatility.

  In the semiconductor single crystal 10, y / x increases from the n-type semiconductor portion 12 toward the p-type semiconductor portion 14, thereby having a p-type semiconductor portion, an n-type semiconductor portion, and a pn junction portion therebetween. The concentration of the constituent element of the clathrate compound represented by the formula (I) is a composition that is inclined from one end side to the other end side, whereby a p-type semiconductor is formed from one end side toward the other end side. Part, pn junction part and n-type semiconductor part are arranged in this order. The semiconductor single crystal of this embodiment having such a structure can generate power in a predetermined temperature range even if there is no temperature difference between the p-type semiconductor portion and the n-type semiconductor portion.

  The power generation method can be performed using a power generation module including the semiconductor single crystal 10 and a pair of electrodes connected to the n-type semiconductor portion 12 and the p-type semiconductor portion 14 respectively. As the configuration other than the semiconductor single crystal 10 of the power generation module, a known configuration can be used. The semiconductor single crystal 10 can generate electric power efficiently by heating to, for example, 50 to 700 ° C., preferably 200 to 500 ° C. In the semiconductor single crystal 10, for example, the absolute value of the potential difference between both ends at 400 ° C. can be 0.3 mV or more, or 0.5 mV or more, and can be 0.3 to 20 mV. It is.

  A method for producing the semiconductor single crystal 10 of the present embodiment will be described below using the clathrate compound of the formula (I) as an example. First, a metal or a semimetal corresponding to the A element, the B element, and the C element that are constituent elements of the formula (I) is prepared. Then, a predetermined amount of the prepared metal and metalloid is weighed according to the composition of the final object. Weighing is performed in a glove box substituted with argon gas as necessary. The weighed metal and antimetal are put into a copper mold and melted by an arc melting method or the like. The temperature of the molten metal during arc melting is, for example, about 3000 ° C.

  When the melt obtained by arc melting is cooled, an ingot of the clathrate compound of formula (I) is obtained. The obtained ingot may be crushed to form particles of a clathrate compound. The particles may be melted in a crucible to produce a single crystal by the Czochralski method. Thereby, the semiconductor single crystal 10 made of the clathrate compound of the formula (I) can be obtained. The obtained semiconductor single crystal 10 may be cut into a desired shape.

  Here, the Czochralski method is a method of obtaining a single crystal by pulling a crystal from the melt in the crucible. When a single crystal of a clathrate compound having a plurality of constituent elements such as formula (I) is produced by the Czochralski method, the component having a smaller density than the component having a higher density is easily pulled and crystallized first. Tend. For this reason, as the production of the single crystal proceeds, the composition of the melt changes. Therefore, in the semiconductor single crystal manufactured by the Czochralski method, the concentration of components having a higher density tends to be lower in the portion formed earlier than in the portion formed later.

  For example, when the B element is Au and the C element is Si, the density of Au is higher in the portion formed later because the density of Au is higher than that of Si. Therefore, in this case, by adjusting the initial mixing ratio of each metal and metalloid, the previously formed portion becomes the n-type semiconductor portion 12 and the later formed portion becomes the p-type semiconductor portion 14.

  FIG. 6 is a diagram schematically illustrating a configuration of a semiconductor single crystal according to another embodiment. The semiconductor single crystal 10a has an n-type semiconductor portion 12 on the upper side and an intrinsic semiconductor portion 16 on the lower side. On the other hand, the semiconductor single crystal 10a does not have a p-type semiconductor portion. The n-type semiconductor portion 12 corresponds to a first semiconductor portion, and the intrinsic semiconductor portion 16 corresponds to a second semiconductor portion.

  In the semiconductor single crystal 10 a, the concentration of a predetermined element changes from the n-type semiconductor portion 12 toward the intrinsic semiconductor portion 16. Similar to the semiconductor single crystal 10, the concentration gradient of such an element contributes to the band gap distribution of the semiconductor single crystal 10a.

  FIGS. 7A and 7B are conceptual diagrams showing a band gap state of the semiconductor single crystal of the present embodiment. 7A and 7B, the vertical axis represents the energy of electrons, and the horizontal axis represents the distance from the end of the semiconductor single crystal on the n-type semiconductor portion 12 side. As shown in FIGS. 7A and 7B, the band gap in the intrinsic semiconductor portion 16 is smaller than the band gap in the n-type semiconductor portion 12. The n-type semiconductor portion 12 is a portion where the Fermi level f is on the conduction band side. The intrinsic semiconductor portion 16 is a portion where the Fermi level f is at the center of the forbidden band between the conduction band and the valence band. The band gap of the semiconductor single crystal 10a may gradually decrease from the end on the n-type semiconductor portion 12 side toward the end on the intrinsic semiconductor portion 16 side.

  FIG. 7A is a conceptual diagram showing a state of thermal excitation when the semiconductor single crystal 10a is heated to a predetermined temperature. As shown in FIG. 7A, when the semiconductor single crystal 10a is heated to a predetermined temperature, electrons in the valence band are thermally excited to the conduction band. At this time, electrons are thermally excited in the conduction band only by the intrinsic semiconductor portion 16 having a relatively small band gap. On the other hand, in the n-type semiconductor part 12 whose band gap is larger than that of the intrinsic semiconductor part 16, electrons are not thermally excited.

  FIG. 7B is a conceptual diagram showing movement of electrons (black circles) when the semiconductor single crystal 10a is heated to a predetermined temperature. As shown in FIG. 7B, the electrons excited in the conduction band move to the lower energy side, that is, the n-type semiconductor portion 12 side. On the other hand, holes (white circles) generated on the valence band side by electron excitation stay in the intrinsic semiconductor portion 16. As a result, the n-type semiconductor portion 12 is negatively charged and the intrinsic semiconductor portion 16 is positively charged, so that an electromotive force is generated. In this way, the semiconductor single crystal 10a can generate power even if there is no temperature difference between the n-type semiconductor portion 12 and the intrinsic semiconductor portion 16.

  The semiconductor single crystal 10a is different from the semiconductor single crystal 10 in which carriers are electrons and holes in that the carriers are only electrons. The semiconductor single crystal 10a of the present embodiment is also useful as the semiconductor single crystal 10 because it can generate power even without a temperature difference. In the semiconductor single crystal 10a, it is not necessary to form a p-type semiconductor portion. For this reason, it becomes easy to produce with the clathrate compound represented by the above formula (I).

  The band gap width (energy gap) and the ratio of the n-type semiconductor part 12 and the intrinsic semiconductor part 16 in the semiconductor single crystal 10a are the same as those of the semiconductor single crystal 10. Further, the material constituting the semiconductor single crystal 10 a may be a clathrate compound represented by the above formula (I) as in the case of the semiconductor single crystal 10. However, since the semiconductor single crystal 10a does not have a p-type semiconductor portion, x in the above formula (I) is 7 to 8, and y is 3.5 to 5.5 or 11 to 16.

  In the semiconductor single crystal 10a, y indicating the molar ratio of the B element in the clathrate compound increases along the direction of the arrow α in FIG. On the other hand, x indicating the molar ratio of the A element may be distributed substantially uniformly in the semiconductor single crystal 10a, or may decrease along the direction of the arrow α in FIG. That is, in the semiconductor single crystal 10a, the value of y / x generally increases along the arrow α direction from the upper end to the lower end in FIG. Therefore, the lower portion has a higher molar ratio (y / x) of the B element to the A element. Thus, the upper portion becomes the n-type semiconductor portion 12 and the lower portion becomes the intrinsic semiconductor portion 16. The value of y / x is higher in the intrinsic semiconductor portion 16 than in the n-type semiconductor portion 12. In the semiconductor single crystal 10a, the value of y / x may gradually decrease from the end on the intrinsic semiconductor portion 16 side toward the end on the n-type semiconductor portion 12 side.

Preferred examples of clathrate _{compound, Ba x Au y Si 46-} y ( where, x is 7 to 8, y is _{3.5~5.5.), Ba x Al y} Si 46-y (where, x is 7 to 8, y is 11 to 16.), and _{Ba x Cu x Si 46-y} ( where, x is 7 to 8, y is from 3.5 to 5.5 .).

  The semiconductor single crystal 10a can be produced in the same manner as the semiconductor single crystal 10, and can be generated by heating to the same temperature. The above description other than the p-type semiconductor portion in the semiconductor single crystal 10 can be applied to the semiconductor single crystal 10a.

  FIG. 8 is a diagram schematically showing a configuration of a semiconductor single crystal according to still another embodiment. The semiconductor single crystal 10b has an intrinsic semiconductor part 16 on the upper side and a p-type semiconductor part 14 on the lower side. On the other hand, the semiconductor single crystal 10b does not have an n-type semiconductor portion. The p-type semiconductor portion 14 corresponds to a first semiconductor portion, and the intrinsic semiconductor portion 16 corresponds to a second semiconductor portion.

  In the semiconductor single crystal 10 b, the concentration of a predetermined element changes from the intrinsic semiconductor portion 16 toward the p-type semiconductor portion 14. Similar to the semiconductor single crystals 10 and 10a, the concentration gradient of such an element contributes to the band gap distribution of the semiconductor single crystal 10b.

  FIGS. 9A and 9B are conceptual diagrams showing the state of the band gap of the semiconductor single crystal of this embodiment. 9A and 9B, the vertical axis represents the energy of electrons, and the horizontal axis represents the distance from the end of the semiconductor single crystal on the intrinsic semiconductor portion 16 side. As shown in FIGS. 9A and 9B, the band gap in the intrinsic semiconductor portion 16 is smaller than the band gap in the p-type semiconductor portion 14. The p-type semiconductor portion 14 is a portion where the Fermi level f is on the valence band side. The intrinsic semiconductor portion 16 is a portion where the Fermi level f is at the center of the forbidden band between the conduction band and the valence band. The band gap of the semiconductor single crystal 10b may gradually increase from the end on the intrinsic semiconductor part 16 side toward the end on the p-type semiconductor part 14 side.

  FIG. 9A is a conceptual diagram showing a state of thermal excitation when the semiconductor single crystal 10b is heated to a predetermined temperature. As shown in FIG. 9A, when the semiconductor single crystal 10b is heated to a predetermined temperature, electrons in the valence band are thermally excited to the conduction band. At this time, electrons are thermally excited in the conduction band only by the intrinsic semiconductor portion 16 having a relatively small band gap. On the other hand, electrons are not thermally excited in the p-type semiconductor portion 14 having a band gap larger than that of the intrinsic semiconductor portion 16.

  FIG. 9B is a conceptual diagram showing movement of holes (white circles) when the semiconductor single crystal 10b is heated to a predetermined temperature. As shown in FIG. 9B, the electrons excited in the conduction band stay on the lower energy side, that is, on the intrinsic semiconductor portion 16 side. On the other hand, holes generated on the valence band side due to excitation of electrons move to the p-type semiconductor portion 14. As a result, the p-type semiconductor portion 14 is positively charged and the intrinsic semiconductor portion 16 is negatively charged, so that an electromotive force is generated. In this way, the semiconductor single crystal 10b can generate power even if there is no temperature difference between the p-type semiconductor portion 14 and the intrinsic semiconductor portion 16.

  The semiconductor single crystal 10b differs from the semiconductor single crystal 10 in which carriers are electrons and holes in that the carriers are only holes. The semiconductor single crystal 10b of the present embodiment is also useful as the semiconductor single crystals 10 and 10a because it can generate power even if there is no temperature difference.

  The band gap width (energy gap) and the ratio of the p-type semiconductor portion 14 and the intrinsic semiconductor portion 16 in the semiconductor single crystal 10 b are the same as those of the semiconductor single crystal 10. Further, the material constituting the semiconductor single crystal 10 a may be a clathrate compound represented by the above formula (I) as in the case of the semiconductor single crystal 10. However, since the semiconductor single crystal 10b does not have an n-type semiconductor portion, x in the above formula (I) is 7 to 8, and y is 5.3 to 6 or 16 to 17.

  In the semiconductor single crystal 10b, y indicating the molar ratio of the B element in the clathrate compound increases along the arrow α direction in FIG. On the other hand, x indicating the molar ratio of the A element may be distributed substantially uniformly in the semiconductor single crystal 10b or may decrease along the direction of the arrow α in FIG. That is, in the semiconductor single crystal 10b, the value of y / x generally increases along the arrow α direction from the upper end to the lower end in FIG. Therefore, the lower portion has a higher molar ratio (y / x) of the B element to the A element. Thus, the upper portion becomes the intrinsic semiconductor portion 16 and the lower portion becomes the p-type semiconductor portion 14. Note that the value of y / x is higher in the p-type semiconductor portion 14 than in the intrinsic semiconductor portion 16. In the semiconductor single crystal 10b, the value of y / x may gradually increase from the end portion on the intrinsic semiconductor portion 16 side toward the end portion on the p-type semiconductor portion 14 side.

Preferred examples of clathrate _{compound, Ba x Au y Si 46-} y ( where, x is 7 to 8, y is _{5.3~6.), Ba x Al y} Si 46-y ( where , X is 7-8, y is 16-17), and Ba _x Cu _x Si _46-y (where x is 7-8 and y is 5.3-6). Is mentioned.

  The semiconductor single crystal 10b can be produced in the same manner as the semiconductor single crystals 10 and 10a, and can be generated by heating to the same temperature. The above description other than the p-type semiconductor portion in the semiconductor single crystal 10 also applies to the semiconductor single crystal 10b.

  FIG. 10 is a diagram schematically showing a configuration of a semiconductor single crystal according to still another embodiment. The semiconductor single crystal 10c includes an n-type semiconductor portion 12 (first semiconductor portion). That is, the semiconductor single crystal 10c is composed only of an n-type semiconductor. In the semiconductor single crystal 10c, the concentration of a predetermined element changes from the upper end 12A (one end) to the lower end 12B (the other end). Similar to the semiconductor single crystals 10, 10a, 10b, the concentration gradient of such elements contributes to the band gap distribution of the semiconductor single crystal 10c.

  FIGS. 11A and 11B are conceptual diagrams showing the state of the band gap of the semiconductor single crystal of the present embodiment. 11A and 11B, the vertical axis represents the energy of electrons, and the horizontal axis represents the distance from the upper end of the semiconductor single crystal 10c. As shown in FIGS. 11A and 11B, the band gap at the lower end 12B of the n-type semiconductor 12 (semiconductor single crystal 10c) is larger than the band gap at the upper end 12A of the n-type semiconductor 12 (semiconductor single crystal 10c). Is also getting smaller. The semiconductor single crystal 10c may have a band gap that gradually decreases from the upper end 12A toward the lower end 12B.

  FIG. 11A is a conceptual diagram showing a state of thermal excitation when the semiconductor single crystal 10c is heated to a predetermined temperature. As shown in FIG. 11A, when the semiconductor single crystal 10c is heated to a predetermined temperature, electrons in the valence band are thermally excited to the conduction band. At this time, electrons are thermally excited in the conduction band only by the lower end portion 12B having a relatively small band gap. On the other hand, electrons are not thermally excited at the upper end portion 12A having a band gap larger than the lower end portion 12B.

  FIG. 11B is a conceptual diagram showing movement of electrons (black circles) when the semiconductor single crystal 10c is heated to a predetermined temperature. As shown in FIG. 11B, the electrons excited in the conduction band move to the upper end portion 12A side. On the other hand, holes (white circles) generated on the valence band side by electron excitation stay on the lower end 12B side. As a result, the upper end portion 12A side is negatively charged and the lower end portion 12B side is positively charged, so that an electromotive force is generated. In this way, the semiconductor single crystal 10c can generate power even if there is no temperature difference between the upper end portion 12A and the lower end portion 12B.

  The semiconductor single crystal 10c is common to the semiconductor single crystal 10a in that the carriers are only electrons. The semiconductor single crystal 10c of this embodiment is also useful as the semiconductor single crystals 10, 10a, and 10b because it can generate power even if there is no temperature difference.

  There is no particular limitation on the band gap width (energy gap) and the ratio of the upper end portion 12A and the lower end portion 12B in the semiconductor single crystal 10c. The ratio of the band gap width (energy gap) of the lower end portion 12B to the band gap width (energy gap) of the upper end portion 12A is preferably small. 0.8 or less may be sufficient as the said ratio, and 0.1-0.7 may be sufficient as it. The smaller this ratio, the wider the temperature range in which power can be generated.

  The material constituting the semiconductor single crystal 10 c may be a clathrate compound represented by the above formula (I), as with the semiconductor single crystal 10. However, since the semiconductor single crystal 10c does not have a p-type semiconductor portion and an intrinsic semiconductor portion, x in the above formula (I) is 7 to 8, and y is 3.5 to 5.5 or 11 to 16. is there.

  In the semiconductor single crystal 10c, y indicating the molar ratio of the B element in the clathrate compound may generally increase along the direction of the arrow α in FIG. On the other hand, x indicating the molar ratio of the element A may be distributed substantially uniformly in the semiconductor single crystal 10c, or may be substantially decreased along the direction of the arrow α in FIG. In the semiconductor single crystal 10c, the value of y / x is larger at the lower end 12B than at the upper end 12A. That is, the lower end portion 12B has a higher molar ratio (y / x) of the B element to the A element than the upper end portion 14A.

  A preferred example of the clathrate compound is the same as that of the semiconductor single crystal 10a. The semiconductor single crystal 10c can be produced in the same manner as the semiconductor single crystal 10a, and can be generated by heating to the same temperature. The description other than the intrinsic semiconductor portion and the p-type semiconductor portion in the semiconductor single crystal 10 also applies to the semiconductor single crystal 10c.

  The semiconductor single crystal shown in FIG. 10 may be a semiconductor single crystal 10 d composed of the p-type semiconductor 14. The semiconductor single crystal 10d includes a p-type semiconductor part 14 (first semiconductor part). That is, the semiconductor single crystal 10d is composed of only a p-type semiconductor. In the semiconductor single crystal 10d, the concentration of a predetermined element changes from the upper end portion 14A (one end portion) toward the lower end portion 14B (the other end portion). Similar to the semiconductor single crystals 10, 10a, 10b, and 10c, the concentration gradient of such an element contributes to the band gap distribution of the semiconductor single crystal 10d.

  12A and 12B are conceptual diagrams showing the band gap state of the semiconductor single crystal 10d. 12A and 12B, the vertical axis represents electron energy, and the horizontal axis represents the distance from the upper end of the semiconductor single crystal 10d. As shown in FIGS. 12A and 12B, the band gap at the upper end portion 14A of the p-type semiconductor 14 (semiconductor single crystal 10d) is larger than the band gap at the lower end portion 14B of the p-type semiconductor 14 (semiconductor single crystal 10d). Is also getting smaller. That is, the semiconductor single crystal 10d may have a band gap that gradually increases from the upper end portion 14A toward the lower end portion 14B.

  FIG. 12A is a conceptual diagram showing a state of thermal excitation when the semiconductor single crystal 10c is heated to a predetermined temperature. As shown in FIG. 12A, when the semiconductor single crystal 10d is heated to a predetermined temperature, electrons in the valence band are thermally excited to the conduction band. At this time, electrons are thermally excited in the conduction band only by the upper end portion 14A having a relatively small band gap. On the other hand, electrons are not thermally excited at the lower end portion 14B having a band gap larger than the upper end portion 14A.

  FIG. 12B is a conceptual diagram showing movement of holes (white circles) when the semiconductor single crystal 10d is heated to a predetermined temperature. As shown in FIG. 12B, holes generated in the valence band by excitation of electrons move to the lower end portion 14B side. On the other hand, electrons excited in the conduction band stay on the upper end portion 14A side. As a result, the upper end portion 14A side is negatively charged and the lower end portion 14B side is positively charged, so that an electromotive force is generated. In this way, the semiconductor single crystal 10d can generate power even if there is no temperature difference between the upper end portion 14A and the lower end portion 14B.

  The semiconductor single crystal 10c is common to the semiconductor single crystal 10b in that the carriers are only holes. The semiconductor single crystal 10d of the present embodiment is also useful as the semiconductor single crystals 10, 10a, 10b, and 10c because it can generate power even if there is no temperature difference.

The band gap width (energy gap) and the ratio of the upper end portion 14A and the lower end portion 14B in the semiconductor single crystal 10d are the same as those of the semiconductor single crystal 10c.
The material constituting the semiconductor single crystal 10d may be a clathrate compound represented by the above formula (I) as in the case of the semiconductor single crystal 10. However, since the semiconductor single crystal 10d does not have an n-type semiconductor portion and an intrinsic semiconductor portion, x in the above formula (I) is 7 to 8, and y is 5.3 to 6 or 16 to 17.

  In the semiconductor single crystal 10d, y indicating the molar ratio of the B element in the clathrate compound may generally increase along the direction of the arrow α in FIG. On the other hand, x indicating the molar ratio of the A element may be distributed substantially uniformly in the semiconductor single crystal 10d, or may be substantially decreased along the direction of the arrow α in FIG. In the semiconductor single crystal 10d, the value of y / x is larger in the lower end portion 14B than in the upper end portion 14A. That is, the lower end portion 14B has a higher molar ratio (y / x) of the B element to the A element than the upper end portion 14A.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments. For example, in the above-described embodiment, a columnar semiconductor single crystal is shown. However, the shape of the semiconductor single crystal of the present invention is not limited to a prismatic shape, and various shapes can be used depending on applications. Moreover, the manufacturing method of a semiconductor single crystal is not limited to the above-mentioned method, The manufacturing method of various single crystals can be applied. For example, by a method of implanting ions such as dopants into a single crystal having a uniform composition, a method of sintering by immersing the single crystal in a melt of a predetermined metal, and providing a concentration difference of the predetermined element in the single crystal, A semiconductor single crystal may be manufactured. In addition, a polycrystalline sample is prepared in advance so that a predetermined element concentration changes, and after the sample is irradiated with a laser beam and dissolved, the sample is gradually cooled to grow a single crystal. Method).

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

Example 1
<Preparation of clathrate compound by arc melting method>
Commercially available Ba powder, Au powder, and Si powder (all high-purity products) were prepared. These powders were weighed so that Ba: Au: Si = 8: 6: 40 (molar ratio). Each weighed powder was placed in a Cu mold and placed in a chamber. After replacing the inside of the chamber with argon gas, it was heated to about 2000 ° C. by the arc melting method to melt the powder in the Cu mold. In this way, a clathrate compound (Ba ₈ Au ₆ Si ₄₀ ) was prepared.

<Preparation of single crystal by Czochralski method>
The prepared clathrate compound was pulverized and granulated, and then placed in an alumina crucible. This alumina crucible was placed in the chamber. The alumina crucible was heated while argon gas was introduced into the chamber at a rate of about 0.5 L / min so that the pressure in the chamber was 1.5 atm, and the clathrate compound was heated to 1112 ° C. to be melted. . One hour after the melting, a shaft provided with Si as a seed crystal was brought into contact with the surface of the melt while rotating at 30 rpm. Then, while lowering the clathrate compound to 1079 ° C., the shaft was pulled up at a speed of 5 mm / hour. In this way, a single crystal of clathrate compound having a bell shape as shown in FIG. 13 was produced. The upper part of FIG. 13 is the pulling direction of the Czochralski method.

<Evaluation of single crystal>
As shown in FIG. 13, the single crystal was cut into almost the same size from the top to the bottom. Seven samples of 1-7 were obtained. In addition, it is cut along the vertical direction of the single crystal, and the plate-like No. 1 is formed with the pulling direction of the Czochralski method as the longitudinal direction. Eight samples were obtained. Using an electron beam microanalyzer (EPMA-1200 (WDX)), No. Elemental analysis of samples 1-7 was performed. At this time, the filament voltage was set to 15 kV and the filament current was set to 10 nA. The measured value of elemental analysis was converted into the composition ratio of the clathrate compound. Table 2 shows the composition ratio.

As shown in Table 2, the concentration of Au was higher and the value of Au / Ba was higher in the lower part than in the upper part of the single crystal. Next, no. Sample 4 was made into powder, and crystal structure analysis was performed by powder X-ray analysis. Specifically, the peak measured using an X-ray diffractometer (RINT-2100) was compared with the peak of the theoretical value calculated using Crystal Diffract 4.1.2. In calculating the theoretical peak, Ba ₈ Au ₆ Si _{40 in} which the 6c site of Ba ₈ Si ₄₆ is replaced with Au is used as a simulation model, and 10.41 (Å) obtained as an actual measurement value as a lattice constant is calculated. Using. The details of the X-ray diffraction measurement conditions are shown in Table 3. FIG. 14A shows the measurement result of X-ray diffraction, and FIG. 14B shows the result of the theoretical value by simulation.

  Comparing FIG. 14A and FIG. 14B, it was confirmed that the peak positions of the measurement result and the theoretical value coincided. From this, it was confirmed that the crystal structure of the sample was a clathrate structure.

  Next, sample no. 1-No. The Seebeck effect of 7 was investigated. Specifically, a lead wire is connected to both ends of each sample in the longitudinal direction (perpendicular to the pulling direction of the Czochralski method), and the temperature is increased while maintaining the temperature difference between both ends at 20 ° C. Seebeck The temperature dependence of the coefficient S (μV / K) was examined. FIG. 15 shows the change in Seebeck coefficient S until the average temperature on the low temperature side and the high temperature side reaches 500 ° C. for each sample. From the results shown in FIG. 1-No. The Seebeck coefficient S of the sample No. 6 is a negative value. The Seebeck coefficient S of the sample of 7 was a positive value. That is, no. 1-No. Sample 6 is an n-type semiconductor. Sample 7 was a p-type semiconductor. From this, No. 6 and no. It can be seen that the boundary portion of the sample No. 7 is a pn junction, and an intrinsic semiconductor portion is formed at the boundary portion.

  Further, according to the result of FIG. The absolute value of the Seebeck coefficient S of the samples 1 to 6 increased at the beginning of the temperature increase and turned to decrease at the predetermined temperature. The temperature at which the increase starts to decrease decreases as the sample number increases. This indicates that the closer to the pn junction, that is, the intrinsic semiconductor portion, the smaller the band gap.

  No. constituting the n-type semiconductor portion. Au / Ba of 1 to 6 is 0.59 to 0.61 (average value: 0.60), and No. 1 constituting the p-type semiconductor portion. The Au / Ba of No. 7 was 0.63 (average value: 0.63). No. corresponding to the intrinsic semiconductor part. 6 and no. The Au / Ba at the boundary portion of the sample No. 7 is 0.62, which is an intermediate value between 0.61 and 0.63. From this, it was confirmed that Au / Ba is the highest in the p-type semiconductor portion and lowest in the n-type semiconductor portion, and the intrinsic semiconductor portion is between the p-type semiconductor portion and the n-type semiconductor portion.

  Next, no. The electromotive force of 8 samples was measured. Specifically, no. Conductive wires were connected to both ends of the sample 8 in the longitudinal direction (the pulling direction of the Czochralski method), heated, and the potential difference between the ends was measured. At this time, the potential difference was measured by heating while preventing temperature from occurring at both ends. The measurement results are shown in FIG. As shown in FIG. 16, it was confirmed that a potential difference was generated by heating to a predetermined temperature or higher even though there was no temperature difference between both ends.

  Thus, it is considered that the potential difference increases as the temperature rises because the number of electrons and holes that can be excited in the pn junction having a small band gap increases due to the increase in thermal energy. That is, the semiconductor single crystal 10 is an n-type semiconductor part in which electrons are excited from the valence band to the conduction band only in the intrinsic semiconductor part of the pn junction in a predetermined temperature range, and the electrons transferred to the conduction band have low energy. Move to the side. On the other hand, holes generated in the valence band in the intrinsic semiconductor portion of the pn junction move to the p-type semiconductor portion side. Due to the bias of this carrier, No. Sample 8 is a power generation material having a p-type semiconductor portion as a positive electrode and an n-type semiconductor portion as a negative electrode.

  On the other hand, no. When the temperature of the sample No. 8 exceeds a predetermined temperature (about 390 ° C. in FIG. 16), the potential difference begins to decrease because of thermal excitation of electrons and holes not only in the pn junction but also in the p-type semiconductor and n-type semiconductor. This is considered to be caused by the reduction in the energy difference between the bands of the p-type semiconductor portion and the n-type semiconductor portion. Therefore, it is considered that if the temperature is continuously raised, the entire semiconductor single crystal 10 reaches the intrinsic region, and a potential difference cannot be obtained.

  Just in case, no. Eight samples were inverted so that the direction of the longitudinal direction was reversed, and the electromotive force in the reverse direction was measured in the same manner. The result is shown in FIG. As shown in FIG. 17, the same result as that shown in FIG. 17 was obtained except that the sign was reversed. From these results, no. It was confirmed that the 14 samples generated a potential difference by heating even if there was no temperature difference between the two ends.

(Example 2)
Except that commercially available Ba powder, Au powder, and Si powder were weighed so as to be Ba: Au: Si = 8: 8: 38 (molar ratio) and placed in a Cu mold, the same as Example 1 was performed. The clathrate compound (Ba ₈ Au ₈ Si ₃₈ ) was prepared by performing arc melting. A single crystal of a clathrate compound having a bell shape as shown in FIG. 18 was produced by the Czochralski method using the prepared clathrate compound in the same manner as in Example 1. The upper part of FIG. 18 is the pulling direction of the Czochralski method.

  As shown in FIG. 18, the single crystal was cut into approximately the same size from the top to the bottom. Eleven samples from 1 to 11 were obtained. In addition, it is cut along the vertical direction of the single crystal, and the plate-like No. 1 is formed with the pulling direction of the Czochralski method as the longitudinal direction. 12 samples were obtained. In the same manner as in Example 1, no. 1-No. Eleven samples were subjected to elemental analysis. The measured value of elemental analysis was converted into the composition ratio of the clathrate compound. Table 4 shows the composition ratio.

As shown in Table 4, the concentration of Au was higher and the value of Au / Ba was larger in the lower part than in the upper part of the single crystal. Next, no. Sample 4 was powdered and crystal structure analysis was performed in the same manner as in Example 1. Use the calculation of the peak of theory, using the _Ba 8 _Au 6 _{Si 38} to the 6c site of _Ba 8 _{Si 46} was replaced with Au as a simulation model, 10.41 obtained in the actual measurement values as the lattice constant a (Å) It was. FIG. 19A shows the measurement result of the X-ray diffractometer, and FIG. 19B shows the result of the theoretical value by simulation.

  Comparison of FIG. 19A and FIG. 19B confirmed that the peak positions of the measurement result and the theoretical value coincided. From this, it was confirmed that the crystal structure of the sample was a clathrate structure. Next, sample no. 2-No. Ten Seebeck effects were examined. Specifically, a lead wire is connected to both ends of each sample in the longitudinal direction (perpendicular to the pulling direction of the Czochralski method), and the temperature is increased while maintaining a temperature difference between both ends at 20 ° C. The temperature dependence of the coefficient S (μV / K) was examined. For each sample, the change in Seebeck coefficient S when the temperature at the end on the low temperature side is raised to 500 ° C. is shown in FIGS.

  As shown in FIG. The Seebeck coefficient S of samples 2 to 5 was a negative value and was an n-type semiconductor. On the other hand, as shown in FIG. The Seebeck coefficient S of samples 6 to 11 was a positive value and was a p-type semiconductor. From this, No. 5 and no. It can be seen that the boundary portion of the sample No. 6 is a pn junction, and an intrinsic semiconductor portion is formed at the boundary portion.

  No. constituting the n-type semiconductor portion. The Au / Ba of 2 to 5 is 0.62 to 0.63 (average value: 0.63), and No. 2 constituting the p-type semiconductor portion. Au / Ba of 6-11 was 0.66-0.69 (average value: 0.68). No. corresponding to the intrinsic semiconductor part. 5 and no. The Au / Ba at the boundary portion of the 6 samples is 0.65, which is an intermediate value between 0.64 and 0.66. From this, it was confirmed that Au / Ba is the highest in the p-type semiconductor portion and lowest in the n-type semiconductor portion, and the intrinsic semiconductor portion is between the p-type semiconductor portion and the n-type semiconductor portion.

  Furthermore, according to the results of FIGS. 2-5 and no. It was confirmed that the absolute values of the Seebeck coefficient S of the samples 7 to 11 increased at the beginning of the temperature increase and started to decrease at a predetermined temperature. No. The sample No. 6 has a peak at room temperature, and therefore, it is considered that the absolute value of the Seebeck coefficient S continues to decrease from the start of temperature increase. Therefore, the temperature at which the absolute value of the Seebeck coefficient S turns from increasing to decreasing is No. In samples 2 to 5, the sample number decreased as the sample number increased. In the samples 6 to 11, it can be said that the sample number decreases as the sample number decreases. This is no. 5 and no. 6 shows that the closer to the intrinsic semiconductor portion to the boundary portion of the 6 samples, the smaller the band gap.

  Next, no. The electromotive force of 12 samples was measured. Specifically, no. Conductive wires were connected to both ends of the twelve samples in the longitudinal direction (the pulling direction of the Czochralski method), respectively, and the potential difference generated between both ends was measured by heating. At this time, the potential difference was measured by heating while preventing a temperature difference between both ends. The measurement results are shown in FIG. As shown in FIG. 22, it was confirmed that a potential difference was generated by heating to a predetermined temperature or higher even though there was no temperature difference between both ends.

  From this result, no. 12 samples were confirmed to be power generation materials having a p-type semiconductor portion as a positive electrode and an n-type semiconductor portion as a negative electrode. That is, no. Twelve samples were confirmed to be useful power generation materials because a potential difference was generated by heating even if there was no temperature difference between both ends.

(Example 3)
Except that commercially available Ba powder, Au powder, and Si powder were weighed so as to be Ba: Au: Si = 8: 8: 38 (molar ratio) and placed in a Cu mold, the same as Example 1 was performed. The clathrate compound (Ba ₈ Au ₈ Si ₃₈ ) was prepared by performing arc melting. Using the prepared clathrate compound, a single crystal of a clathrate compound having a shape as shown in FIG. 23 was produced by the Czochralski method in the same manner as in Example 1. The upper part of FIG. 23 is the pulling direction of the Czochralski method.

  As shown in FIG. 23, the single crystal was cut into approximately the same size from the top to the bottom. Four samples of 13-16 were obtained. In addition, it is cut along the vertical direction of the single crystal, and the plate-like No. 1 is formed with the pulling direction of the Czochralski method as the longitudinal direction. Seventeen samples were obtained. In the same manner as in Example 1, no. 13-No. Elemental analysis of 16 samples was performed. The measured value of elemental analysis was converted into the composition ratio of the clathrate compound. Table 5 shows the composition ratio.

  As shown in Table 5, the concentration of Au was higher and the value of Au / Ba was larger in the lower part than in the upper part of the single crystal. Next, no. 13-No. Sixteen samples were examined for Seebeck effect. Specifically, a lead wire is connected to both ends of each sample in the longitudinal direction (perpendicular to the pulling direction of the Czochralski method), and the temperature is increased while maintaining a temperature difference between both ends at 20 ° C. The temperature dependence of the coefficient S (μV / K) was examined. FIG. 24 shows the change in Seebeck coefficient S when each sample is heated.

  As shown in FIG. The Seebeck coefficient S of samples 13 and 14 was a negative value and was an n-type semiconductor. No. The Seebeck coefficient of the 15 samples was in the range of negative values to 0. No. The Seebeck coefficient S of 16 samples was a positive value and was a p-type semiconductor. From this, No. 15 and No. The boundary part of 16 samples is a pn junction part, and it is thought that the intrinsic semiconductor part is formed in the boundary part.

  No. constituting the n-type semiconductor portion. The Au / Ba of Nos. 13 and 14 is 0.63, and No. constituting the p-type semiconductor portion. 16 Au / Ba was 0.65. No. corresponding to the intrinsic semiconductor part. 15 and No. Au / Ba at the boundary portion of the 16 samples is 0.64, which is an intermediate value between 0.63 and 0.65. From this, it was confirmed that Au / Ba is the highest in the p-type semiconductor portion and lowest in the n-type semiconductor portion, and the intrinsic semiconductor portion is between the p-type semiconductor portion and the n-type semiconductor portion.

  Furthermore, according to the result of FIG. It was confirmed that the absolute values of the Seebeck coefficient S of the samples 13, 14, 15, and 16 increased at the beginning of the temperature increase and started to decrease at a predetermined temperature. No. Since the sample No. 15 has a peak at normal temperature, it is considered that the absolute value of the Seebeck coefficient S continues to decrease consistently from the start of temperature increase. Therefore, the temperature at which the absolute value of the Seebeck coefficient S turns from increasing to decreasing is No. In samples 13 and 14, the sample number decreased as the sample number increased. In samples 15 and 16, it can be said that the sample number decreases as the sample number decreases. This is no. The closer to 15, the smaller the band gap.

  Next, no. The electromotive force of 17 samples was measured. FIG. 25 is a diagram for explaining an electromotive force measurement method. No. The end 17a of the sample No. 17 is No. 13 samples have the composition of the upper end side (the end opposite to the No. 14 side). On the other hand, no. The end 17b of the sample No. 17 is 15 and No. It has a composition of 16 sample boundaries. That is, no. The sample 17 is a semiconductor single crystal including an n-type semiconductor portion on the end portion 17a side and an intrinsic semiconductor portion on the end portion 17b side.

  As shown in FIG. Conductive wires were connected to both ends in the longitudinal direction of 17 samples (the pulling direction of the Czochralski method), respectively, and the potential difference generated between both ends was measured by heating. At this time, the potential difference was measured by heating while preventing a temperature difference between both ends. The measurement results are shown in FIG. As shown in FIG. 26, it was confirmed that a potential difference was generated by heating even though there was no temperature difference between both ends. From this result, no. It was confirmed that the sample 17 was a power generation material having the intrinsic semiconductor portion as the positive electrode and the n-type semiconductor portion as the negative electrode.

  No. When the temperature of the sample 17 exceeds a predetermined temperature (about 450 ° C. in FIG. 26), the absolute value of the potential difference starts to decrease not only in the intrinsic semiconductor portion but also in the n-type semiconductor portion due to thermal excitation of electrons and holes. This is considered to be due to the reduction in the energy difference between the bands of the intrinsic semiconductor portion and the n-type semiconductor portion. Therefore, it is considered that when the temperature continues to rise, the entire semiconductor single crystal reaches the intrinsic region, and a potential difference cannot be obtained.

Example 4
Except that the commercially available Ba powder, Cu powder, and Si powder were weighed so as to be Ba: Cu: Si = 8: 6: 40 (molar ratio) and put in a Cu mold, the same as in Example 1. The clathrate compound (Ba ₈ Cu ₆ Si ₄₀ ) was prepared by performing arc melting. A single crystal of a clathrate compound having a shape as shown in FIG. 27 was produced by the Czochralski method using the prepared clathrate compound in the same manner as in Example 1. The upper part of FIG. 27 is the pulling direction of the Czochralski method.

  As shown in FIG. 27, the single crystal was cut into almost the same size from the top to the bottom. Five samples of 18-22 were obtained. In addition, it is cut along the vertical direction of the single crystal, and the plate-like No. 1 is formed with the pulling direction of the Czochralski method as the longitudinal direction. 23 samples were obtained. In the same manner as in Example 1, no. 18-No. Elemental analysis of 22 samples was performed. The measured value of elemental analysis was converted into the composition ratio of the clathrate compound. Table 6 shows the composition ratio.

  As shown in Table 6, the lower portion of the single crystal had a higher Cu concentration and a higher Cu / Ba value. Next, sample no. 18-No. 22 Seebeck effects were examined. Specifically, a lead wire is connected to both ends of each sample in the longitudinal direction (perpendicular to the pulling direction of the Czochralski method), and the temperature is increased while maintaining a temperature difference between both ends at 20 ° C. The temperature dependence of the coefficient S (μV / K) was examined. FIG. 28 shows the change in the Seebeck coefficient S when the temperature at the end on the low temperature side is raised to 700 ° C. for each sample.

  As shown in FIG. The Seebeck coefficient S of samples 18 to 22 was a negative value and was an n-type semiconductor. No. corresponding to the upper end. The Cu / Ba of No. 18 is 0.57. The Cu / Ba of 22 was 0.58. From this, it was confirmed that Cu / Ba is larger at the lower end than at the upper end.

  Next, no. The electromotive force of 23 samples was measured. Specifically, no. Conductive wires were connected to both ends of the 23 samples in the longitudinal direction (the pulling direction of the Czochralski method), and the potential difference generated between the ends was measured by heating. At this time, the potential difference was measured by heating while preventing a temperature difference between both ends. The measurement results are shown in FIG. As shown in FIG. 29, it was confirmed that a potential difference was generated by heating to a predetermined temperature or higher despite no temperature difference between both ends.

  According to the result shown in FIG. Samples 18 to 22 were all n-type semiconductors. Therefore, no. The sample 23 is a semiconductor single crystal made only of an n-type semiconductor. As shown in FIG. In the sample No. 23, even when there was no temperature difference between both ends, a potential difference was generated by heating. From this, No. The 23 samples were confirmed to have a smaller band gap at one end than at the other end. Therefore, no. Sample No. 23 is a power generation material having one end as a positive electrode and the other electrode as a negative electrode.

  ADVANTAGE OF THE INVENTION According to this invention, even if there is no temperature difference between each semiconductor part, the semiconductor single crystal which can generate electric power in a predetermined temperature range can be provided. In addition, by using such a semiconductor single crystal, it is possible to provide a power generation method capable of efficiently generating power in a predetermined temperature range.

  DESCRIPTION OF SYMBOLS 10, 10a, 10b, 10c, 10d ... Semiconductor single crystal, 12 ... n-type semiconductor part (n-type semiconductor), 14 ... p-type semiconductor part (p-type semiconductor), 16 ... intrinsic semiconductor part.

Claims (16)

an n-type semiconductor portion, a p-type semiconductor portion, and an intrinsic semiconductor portion between them;
A semiconductor single crystal in which the intrinsic semiconductor portion has a smaller band gap than the n-type semiconductor portion and the p-type semiconductor portion.   2. The semiconductor single crystal according to claim 1, wherein the concentration of at least one element is higher in the order of the p-type semiconductor portion, the intrinsic semiconductor portion, and the n-type semiconductor portion. The semiconductor single crystal of Claim 1 or 2 containing the clathrate compound represented by following formula (I).
_{A x B y C 46-y} (I)
(In the formula, A represents at least one element selected from the group consisting of Ba, Na, Sr and K, and B represents at least one element selected from the group consisting of Au, Ag, Cu, Ni and Al) C represents at least one element selected from the group consisting of Si, Ge and Sn, x is 7 to 8, y is 3.5 to 6 or 11 to 17, and y / x is (The order is higher in the order of the p-type semiconductor portion, the intrinsic semiconductor portion, and the n-type semiconductor portion.) The semiconductor single crystal of Claim 1 or 2 containing the clathrate compound represented by following formula (II).
Ba _x Au _y Si _46-y (II)
(Wherein x is 7 to 8, y is 3.5 to 6, and y / x is higher in the order of the p-type semiconductor portion, the intrinsic semiconductor portion, and the n-type semiconductor portion). a first semiconductor part comprising an n-type semiconductor part or a p-type semiconductor part;
A semiconductor single crystal in which one end portion and the other end portion of the first semiconductor portion are different in band gap. The semiconductor single crystal of Claim 5 containing the clathrate compound represented by following formula (I).
_{A x B y C 46-y} (I)
(In the formula, A represents at least one element selected from the group consisting of Ba, Na, Sr and K, and B represents at least one element selected from the group consisting of Au, Ag, Cu, Ni and Al) C represents at least one element selected from the group consisting of Si, Ge, and Sn, and when the first semiconductor portion is the n-type semiconductor portion, x is 7 to 8 and y is 3 5 to 5.5 or 11 to 16. When the first semiconductor portion is the p-type semiconductor portion, x is 7 to 8 and y is 5.3 to 6 or 16 to 17. Y / x is different at one end and the other end.) The semiconductor single crystal of Claim 5 containing the clathrate compound represented by following formula (II).
Ba _x Au _y Si _46-y (II)
(In the formula, when the first semiconductor part is composed of the n-type semiconductor part, x is 7 to 8, and y is 3.5 to 5.5 or 11 to 16. The first semiconductor part. Is composed of the p-type semiconductor portion, x is 7 to 8, and y is 5.3 to 6 or 16 to 17. y / x is different at one end and the other end.) A second semiconductor part composed of an intrinsic semiconductor part adjacent to the first semiconductor part;
The semiconductor single crystal according to claim 5, wherein the second semiconductor part has a smaller band gap than the first semiconductor part. The semiconductor single crystal according to claim 8, wherein the first semiconductor part and the second semiconductor part contain a clathrate compound represented by the following formula (I).
_{A x B y C 46-y} (I)
(In the formula, A represents at least one element selected from the group consisting of Ba, Na, Sr and K, and B represents at least one element selected from the group consisting of Au, Ag, Cu, Ni and Al) C represents at least one element selected from the group consisting of Si, Ge, and Sn, and when the first semiconductor portion is an n-type semiconductor portion, x is 7 to 8, and y is 3.5 to 5.5 or 11 to 16, and y / x is higher in the intrinsic semiconductor part than in the n-type semiconductor part, and when the first semiconductor part is composed of a p-type semiconductor part, x is 7 to 8 Y is 5.3 to 6 or 16 to 17, and y / x is higher in the p-type semiconductor part than in the intrinsic semiconductor part.) The semiconductor single crystal according to claim 8, wherein the first semiconductor portion and the second semiconductor portion include a clathrate compound represented by the following formula (II).
Ba _x Au _y Si _46-y (II)
(In the formula, when the first semiconductor portion is an n-type semiconductor portion, x is 7 to 8, y is 3.5 to 5.5, or 11 to 16, and y / x is the intrinsic semiconductor portion. When the first semiconductor part is a p-type semiconductor part, x is 7 to 8, y is 5.3 to 6 or 16 to 17, and y / x (The p-type semiconductor portion is higher than the intrinsic semiconductor portion.)   The semiconductor single crystal according to any one of claims 1 to 10, wherein an absolute value of a potential difference between both ends at 400 ° C is 0.3 mV or more. a semiconductor single crystal having an n-type semiconductor portion, a p-type semiconductor portion, and an intrinsic semiconductor portion therebetween,
A semiconductor single crystal comprising a clathrate compound represented by the following formula (I).
_{A x B y C 46-y} (I)
(In the formula, A represents at least one element selected from the group consisting of Ba, Na, Sr and K, and B represents at least one element selected from the group consisting of Au, Ag, Cu, Ni and Al) C represents at least one element selected from the group consisting of Si, Ge and Sn, x is 7 to 8, y is 3.5 to 6 or 11 to 17, and y / x is (The order is higher in the order of the p-type semiconductor portion, the intrinsic semiconductor portion, and the n-type semiconductor portion.) a first semiconductor part comprising an n-type semiconductor part or a p-type semiconductor part;
A semiconductor single crystal comprising a clathrate compound represented by the following formula (I).
_{A x B y C 46-y} (I)
(In the formula, A represents at least one element selected from the group consisting of Ba, Na, Sr and K, and B represents at least one element selected from the group consisting of Au, Ag, Cu, Ni and Al) C represents at least one element selected from the group consisting of Si, Ge, and Sn, and when the first semiconductor portion is made of the n-type semiconductor, x is 7 to 8, and y is 3. 5 to 5.5 or 11 to 16. When the first semiconductor portion is made of the p-type semiconductor, x is 7 to 8, and y is 5.3 to 6 or 16 to 17. / X is different at one end and the other end of the semiconductor single crystal.) A second semiconductor portion made of an intrinsic semiconductor portion so as to be adjacent to the first semiconductor portion, wherein the intrinsic semiconductor portion includes a clathrate compound represented by the formula (I);
When the first semiconductor part is composed of the n-type semiconductor part, y / x is higher in the intrinsic semiconductor part than in the n-type semiconductor part,
14. The semiconductor single crystal according to claim 13, wherein when the first semiconductor part is composed of the p-type semiconductor part, y / x is higher in the p-type semiconductor part than in the intrinsic semiconductor part. The semiconductor single crystal according to claim 12, wherein the clathrate compound is a compound represented by the formula (II).
Ba _x Au _y Si _46-y (II)
(In the formula, x is 7 to 8, and y is 3.5 to 6.)   A power generation method for generating power by heating the semiconductor single crystal according to any one of claims 1 to 15.