Thermoelectric conversion material, thermoelectric conversion element, thermoelectric conversion module, and optical sensor
A thermoelectric conversion material includes: a base material that is a semiconductor composed of a base material element; a first additional element that is an element different from the base material element, has a vacant orbital in a d orbital or f orbital located internal to an outermost shell of the first additional element and forms a first additional level in a forbidden band of the base material; and a second additional element that is an element different from both of the base material element and the first additional element and forms a second additional level in the forbidden band of the base material. A difference is 1 between the number of electrons in an outermost shell of the second additional element and the number of electrons in at least one outermost shell of the base material element.
1. A thermoelectric conversion material comprising:
a base material that is a semiconductor composed of a base material element;
a first additional element, the first additional element being an element different from the base material element, the first additional element having a vacant orbital in a d orbital or f orbital located internal to an outermost shell of the first additional element, the first additional element forming a first additional level in a forbidden band of the base material; and
a second additional element, the second additional element being an element different from both of the base material element and the first additional element, the second additional element forming a second additional level in the forbidden band of the base material, wherein
a difference is 1 between the number of electrons in an outermost shell of the second additional element and the number of electrons in at least one outermost shell of the base material element,
wherein a structure of the thermoelectric conversion material comprises a crystal phase of the base material, a crystal phase including the first additional element and a crystal phase including the second additional element,
wherein a ratio of a crystal phase including at least one of the first additional element and the second additional element to a whole of the structure of the thermoelectric conversion material is less than or equal to 6.0 volume %,
wherein the base material is a SiGe-based material,
wherein a ratio of an energy difference between a valence band of the base material and the first additional level at a position closest to the valence band of the base material to a band gap of the base material is more than or equal to 20%,
wherein a ratio of an energy difference between a conduction band of the base material and the first additional level at a position closest to the conduction band of the base material to the band gap of the base material is more than or equal to 20%, and
wherein the first additional element is Fe, Cu, Ni, Mn, Cr, V, Ti, Ag, Pd, Pt, or Ir.
2. The thermoelectric conversion material according to claim 1 , wherein a crystal phase having a grain size of less than or equal to 50 nm and composed of the base material element is included in the structure of the thermoelectric conversion material.
3. The thermoelectric conversion material according to claim 2 , wherein a ratio of an intensity of a peak having a maximum intensity in peaks each indicating a crystal phase including at least one of the first additional element and the second additional element, to an intensity of a peak having a maximum intensity in peaks each indicating a crystal phase composed of the base material element is less than or equal to 2.0% in an X-ray diffraction pattern of the thermoelectric conversion material.
4. The thermoelectric conversion material according to claim 2 , wherein
the structure of the thermoelectric conversion material includes an amorphous phase including the base material element as a main component,
wherein a crystal phase composed of the base material element exists in the amorphous phase, and
wherein the crystal phase is a microcrystal which exists in the amorphous phase in a dispersed manner.
5. The thermoelectric conversion material according to claim 1 , wherein the first additional element is a transition metal.
6. The thermoelectric conversion material according to claim 1 , wherein the second additional level exists between the first additional level and an energy band that is one of a valence band and a conduction band each adjacent to the forbidden band of the base material, the one of the valence band and the conduction band being close to the first additional level relative to the other of the valence band and the conduction band.
7. The thermoelectric conversion material according to claim 1 , wherein a density of states of the first additional level has a ratio of more than or equal to 0.1 with respect to a maximum value of a density of states in a valence band adjacent to the forbidden band of the base material.
8. The thermoelectric conversion material according to claim 1 , wherein a content ratio of the first additional element is more than or equal to 0.1 at % and less than or equal to 5 at %.
9. The thermoelectric conversion material according to claim 1 , wherein
the first additional element is Cu, and
the second additional element is B.
10. A thermoelectric conversion material comprising,
a base material that is a semiconductor composed of a base material element;
a first additional element, the first additional element being an element different from the base material element, the first additional element having a vacant orbital in a d orbital or f orbital located internal to an outermost shell of the first additional element, the first additional element forming a first additional level in a forbidden band of the base material; and
a second additional element, the second additional element being an element different from both of the base material element and the first additional element, the second additional element forming a second additional level in the forbidden band of the base material, wherein
a difference is 1 between the number of electrons in an outermost shell of the second additional element and the number of electrons in at least one outermost shell of the base material element,
wherein a structure of the thermoelectric conversion material comprises a crystal phase of the base material, a crystal phase including the first additional element and a crystal phase including the second additional element, and
wherein a ratio of a crystal phase including at least one of the first additional element and the second additional element to a whole of the structure of the thermoelectric conversion material is less than or equal to 6.0 volume %,
wherein
the first additional element is Fe, and
the second additional element is P.
11. A thermoelectric conversion element comprising:
a thermoelectric conversion material portion;
a first electrode disposed in contact with the thermoelectric conversion material portion; and
a second electrode disposed in contact with the thermoelectric conversion material portion and disposed to be separated from the first electrode, wherein
the thermoelectric conversion material portion is composed of the thermoelectric conversion material recited in claim 1 , the thermoelectric conversion material being adjusted in component composition to have p type or n type conductivity.
12. A thermoelectric conversion module comprising a plurality of the thermoelectric conversion elements recited in claim 11 .
13. An optical sensor comprising:
an absorber that absorbs optical energy; and
a thermoelectric conversion material portion connected to the absorber, wherein
the thermoelectric conversion material portion is composed of the thermoelectric conversion material recited in claim 1 , the thermoelectric conversion material being adjusted in component composition to have p type or n type conductivity.
14. A thermoelectric conversion material comprising:
a base material that is a semiconductor composed of a base material element;
a first additional element, the first additional element being an element different from the base material element, the first additional element having a vacant orbital in a d orbital or f orbital located internal to an outermost shell of the first additional element, the first additional element forming a first additional level in a forbidden band of the base material; and
a second additional element, the second additional element being an element different from both of the base material element and the first additional element, the second additional element forming a second additional level in the forbidden band of the base material, wherein
a difference is 1 between the number of electrons in an outermost shell of the second additional element and the number of electrons in at least one outermost shell of the base material element,
wherein a crystal phase having a grain size of less than or equal to 50 nm and composed of the base material element is included in a structure of the thermoelectric conversion material,
wherein a ratio of an intensity of a peak having a maximum intensity in peaks each indicating a crystal phase including at least one of the first additional element and the second additional element, to an intensity of a peak having a maximum intensity in peaks each indicating a crystal phase composed of the base material element is less than or equal to 2.0% in an X-ray diffraction pattern of the thermoelectric conversion material,
wherein the base material is a SiGe-based material,
wherein a ratio of an energy difference between a valence band of the base material and the first additional level at a position closest to the valence band of the base material to a band gap of the base material is more than or equal to 20%,
wherein a ratio of an energy difference between a conduction band of the base material and the first additional level at a position closest to the conduction band of the base material to the band gap of the base material is more than or equal to 20%, and
wherein the first additional element is Fe, Cu, Ni, Mn, Cr, V, Ti, Ag, Pd, Pt, or Ir.