Atomic force battery

Abstract

To provide a nuclear battery utilizing diamond by which deterioration of diode characteristics caused by increase in diode area is suppressed.SOLUTION: A nuclear battery at least comprises: a laminate having a semiconductor substrate, a metal doped diamond layer, an active layer, and a radioactive substance-containing layer in this order; and an electrode electrically connected with the laminate.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a nuclear battery that utilizes diamond. [Background technology]

[0002] 2. Description of the Related Art Nuclear batteries are known, which generate electromotive force by converting radiation continuously emitted by the nuclear decay of radioactive materials such as radioisotopes into electricity using thermoelectric elements or photoelectric conversion elements.

[0003] Nuclear batteries can generate electricity for extremely long periods of time, such as several decades, by using radioisotopes with long half-lives as radioactive materials. In addition, because they do not use chemical reactions, they can operate even at low temperatures, and are therefore used, for example, as a power source for observation equipment in polar regions and artificial satellites. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2011 / 0031572 Summary of the Invention [Problem to be solved by the invention]

[0005] Diamond has a high dielectric breakdown field (>10MV / cm) and high carrier mobility (electrons: 4500cm 2 / Vs, hole: 3800cm 2 / Vs) and the highest thermal conductivity of any substance (22 W / cmK). In addition, it has excellent chemical stability and radiation resistance, so it is expected to be used as a power device material that operates at high temperatures and in extreme environments.

[0006] The present inventors have studied atomic batteries using diamond. However, when a diamond film is formed on a semiconductor substrate to fabricate a diamond diode, there is a problem that the diode characteristics deteriorate significantly as the diode area increases, and it was thought that it would be difficult to increase the diode area and use diamond in an atomic battery.

[0007] A main object of the present invention is to provide a nuclear battery that utilizes diamond and that suppresses the deterioration of diode characteristics that accompanies an increase in the diode area. [Means for solving the problem]

[0008] The present inventors have carried out intensive research to solve the above-mentioned problems. As a result, they have found that in the configuration of nuclear battery, by disposing a metal-doped diamond layer between a semiconductor substrate and an active layer, the deterioration of diode characteristics accompanying the increase in the area of ​​diode can be suitably suppressed. Based on these findings, the present invention is an invention that has been completed through further research.

[0009] That is, the present invention provides the following aspects. Item 1. A laminate having at least a semiconductor substrate, a metal-doped diamond layer, an active layer, and a radioactive substance-containing layer in this order; an electrode electrically connected to the laminate; A nuclear battery comprising: Item 2. The nuclear battery according to item 1, wherein the active layer is formed of impurity-doped diamond. Item 3. The metal-doped diamond layer has a metal concentration of 1×10 18 cm -3 More than 1×10 21 cm -3 Item 3. The nuclear battery according to item 1 or 2, which is as follows: Item 4. The nuclear battery according to any one of Items 1 to 3, wherein the thickness of the metal-doped diamond layer is 1 μm or more and 10 μm or less. Item 5. The nuclear battery according to any one of Items 1 to 4, wherein the semiconductor substrate is a single crystal diamond substrate, a polycrystalline diamond substrate, a silicon substrate, a silicon carbide substrate, a gallium nitride substrate, an aluminum nitride substrate, a gallium oxide substrate, or an yttria-stabilized zirconia substrate. Item 6. The nuclear battery according to any one of Items 1 to 5, wherein the metal-doped diamond layer is a p-type semiconductor. Item 7. The nuclear battery according to Item 6, wherein the semiconductor substrate is a p-type semiconductor. Item 8. The nuclear battery according to item 6 or 7, wherein the active layer is an n-type semiconductor. Item 9. The nuclear battery according to any one of Items 1 to 5, wherein the metal-doped diamond layer is an n-type semiconductor. Item 10. The nuclear battery according to Item 9, wherein the semiconductor substrate is an n-type semiconductor. Item 11. The nuclear battery according to item 9 or 10, wherein the active layer is a p-type semiconductor. Item 12. The nuclear battery according to any one of Items 1 to 11, wherein the metal-doped diamond layer and the active layer are in direct contact with each other. Item 13. The nuclear battery according to any one of Items 1 to 11, further comprising an intrinsic semiconductor layer between the metal-doped diamond layer and the active layer. Effect of the Invention

[0010] According to the present invention, it is possible to provide a nuclear battery that utilizes diamond and in which the deterioration of diode characteristics due to an increase in the diode area is suppressed. [Brief description of the drawings]

[0011] [Figure 1] 1 is a graph showing an evaluation of the rectification characteristics (relationship between current (A) and voltage (V)) of the Schottky barrier diodes (Schottky electrode diameter 100 μm) obtained in Example 1 and Comparative Example 1. [Diagram 2]1 is a graph showing the rectification characteristics evaluation (relationship between current (A) and voltage (V)) of the Schottky barrier diode (Schottky electrode diameter 700 μm) obtained in Example 2. [Diagram 3] 1 is a graph showing a predicted characteristic evaluation (relationship between current (A) and voltage (V)) when the Schottky barrier diode obtained in Example 2 is irradiated with an electron beam. [Figure 4] 1 is a graph showing the rectification characteristics evaluation (relationship between current (A) and voltage (V)) of the Schottky barrier diode (Schottky electrode diameter 1000 μm) obtained in Example 2. [Diagram 5] 1 is a graph showing a predicted characteristic evaluation (relationship between current (A) and voltage (V)) when the Schottky barrier diode obtained in Example 2 is irradiated with an electron beam. [Figure 6] FIG. 2 is a schematic diagram showing an example of a Schottky barrier diode structure applied to the nuclear battery of the present invention. [Figure 7] FIG. 2 is a schematic diagram showing an example of a Schottky barrier diode structure applied to the nuclear battery of the present invention. [Figure 8] FIG. 2 is a schematic diagram showing an example of a Schottky barrier diode structure applied to the nuclear battery of the present invention. [Figure 9] FIG. 2 is a schematic diagram showing an example of a Schottky barrier diode structure applied to the nuclear battery of the present invention. [Figure 10] FIG. 2 is a schematic diagram showing an example of a pn junction diode structure applied to the nuclear battery of the present invention. [Figure 11] FIG. 2 is a schematic diagram showing an example of a pn junction diode structure applied to the nuclear battery of the present invention. [Figure 12] FIG. 2 is a schematic diagram showing an example of a pn junction diode structure applied to the nuclear battery of the present invention. [Figure 13] FIG. 2 is a schematic diagram showing an example of a pn junction diode structure applied to the nuclear battery of the present invention. [Figure 14] FIG. 2 is a schematic diagram showing an example of a pin junction diode structure applied to the nuclear battery of the present invention. [Figure 15] FIG. 2 is a schematic diagram showing an example of a pin junction diode structure applied to the nuclear battery of the present invention. [Figure 16] FIG. 2 is a schematic diagram showing an example of a pin junction diode structure applied to the nuclear battery of the present invention. [Figure 17] FIG. 2 is a schematic diagram showing an example of a pin junction diode structure applied to the nuclear battery of the present invention. [Figure 18] FIG. 2 is a schematic diagram of the Schottky barrier diode structure obtained in Example 1. [Figure 19] FIG. 2 is a schematic diagram of a Schottky barrier diode structure obtained in Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The nuclear battery of the present invention is characterized by comprising a laminate having at least a semiconductor substrate, a metal-doped diamond layer, an active layer, and a radioactive material-containing layer in this order, and an electrode electrically connected to the laminate.By comprising such a configuration, the nuclear battery of the present invention suppresses the deterioration of diode characteristics that accompanies the increase in the area of ​​the diode in the nuclear battery using diamond.The nuclear battery of the present invention will be described in detail below.

[0013] In the nuclear battery of the present invention, the semiconductor substrate, the metal-doped diamond layer, the active layer, and the radioactive substance-containing layer are stacked in this order, and the electrode for extracting the electromotive force generated by the emission of radiation to the radioactive substance-containing layer is electrically connected to these stacked bodies (diode structure).

[0014] In the nuclear battery of the present invention, one of the features is that a metal-doped diamond layer is provided between a semiconductor substrate and an active layer.Therefore, when forming a laminate by stacking each layer including an active layer on a semiconductor substrate by vapor deposition, defects are unlikely to be formed in the active layer, and it is considered that the deterioration of the diode characteristics due to the increase in the area of ​​the diode is suppressed.That is, by arranging a metal-doped diamond layer, which was not provided in the conventional technology, between a semiconductor substrate and an active layer, compared with the case where an active layer is stacked on a semiconductor substrate, the defects caused by the structure of the semiconductor substrate are unlikely to be inherited by the active layer, and as a result, defects are unlikely to be formed in the active layer, and it is considered that the deterioration of the diode characteristics due to the increase in the area of ​​the diode is suppressed.

[0015] In the nuclear power battery of the present invention, the structure of a conventional nuclear power battery using diamond can be applied, except that a metal-doped diamond layer is disposed between the semiconductor substrate and the active layer.

[0016] The semiconductor substrate, the metal-doped diamond layer, the active layer, the radioactive material-containing layer and the electrodes, which are particularly important in the nuclear battery of the present invention, will be described in detail below.

[0017] (Semiconductor Substrate) In the present invention, the semiconductor substrate is a layer made of semiconductor material, which is a substrate for laminating layers such as metal-doped diamond layer and active layer.As the semiconductor substrate, there is no particular limitation as long as it does not impair the effect of the present invention, and for example, the semiconductor substrate used in conventional nuclear batteries can also be used in the present invention.Specific examples of the semiconductor substrate include single crystal diamond substrate, polycrystalline diamond substrate, silicon substrate, silicon carbide substrate, gallium nitride substrate, aluminum nitride substrate, gallium oxide substrate, or yttria-stabilized zirconia substrate.

[0018] The semiconductor substrate may be insulating or conductive. When the semiconductor substrate is conductive, it may be a p-type semiconductor (p-type conductivity) or an n-type semiconductor (n-type conductivity). For example, when the semiconductor substrate is a p-type semiconductor (p-type conductivity), the metal-doped diamond layer laminated on the semiconductor substrate is also a p-type semiconductor. Also, for example, when the semiconductor substrate is an n-type semiconductor (n-type conductivity), the metal-doped diamond layer laminated on the semiconductor substrate is also an n-type semiconductor.

[0019] The thickness of the semiconductor substrate can be appropriately set depending on the size of the nuclear battery, and is, for example, about 10 to 1000 μm, preferably about 10 to 200 μm, and more preferably about 10 to 100 μm.

[0020] Furthermore, the area of ​​one side of the semiconductor substrate (the area of ​​one side on which the metal-doped diamond layer is laminated) can be appropriately set depending on the size of the nuclear battery, and a larger area is preferable since it leads to improved output.

[0021] On one surface of the semiconductor substrate, at least a metal-doped diamond layer, an active layer, and a radioactive substance-containing layer are laminated in this order.

[0022] (Metal-doped diamond layer) The metal-doped diamond layer is formed by forming the diamond layer by deposition so that the metal element is included in the diamond crystal. Specifically, the diamond layer is formed by the hot filament CVD method using the metal filament, so that the metal constituting the metal filament is included in the diamond layer, and the metal-doped diamond layer is formed. The method of forming the diamond layer (diamond film) doped with the metal by the hot filament CVD method can be adopted by a known method. A specific example of the method of forming the metal diamond layer doped with the metal by the hot filament CVD method will be described later.

[0023] Specific examples of the metal elements contained in the metal-doped diamond layer include tungsten, tantalum, rhenium, and ruthenium.

[0024] The concentration of the metal element in the metal-doped diamond layer is not particularly limited, but is, for example, 1×10 18 ~1×10 22 cm -3 in the range of about 1×10 19 ~1×10 22 cm -3 in the range of about 1×10 19 ~1×10 21 cm -3 in the range of about 1×10 20 ~1×10 21 cm -3 The concentration of the metal element in the metal-doped diamond layer is a value measured by secondary ion mass spectrometry (SIMS).

[0025] When the metal-doped diamond layer is to be a p-type semiconductor, the metal-doped diamond layer is made to contain impurities such as boron element. For example, when forming the metal-doped diamond layer by the above-mentioned hot filament CVD method, the boron source gas (trimethylboron, etc.) can be made to coexist with the carbon source gas (methane, etc.) to make the metal-doped diamond layer contain boron element, etc. The boron concentration in the metal-doped diamond layer can be, for example, 1×10 18 ~1×10 22 cm -3 in the range of about 1×10 18 ~1×10 21 cm -3 in the range of about 1×10 19 ~1×10 21 cm -3 in the range of about 1×10 20 ~1×10 21 cm -3The concentration of boron element in the metal-doped diamond layer is a value measured by secondary ion mass spectrometry (SIMS).

[0026] In addition, when the metal-doped diamond layer is to be an n-type semiconductor, the metal-doped diamond layer is doped with impurities such as phosphorus. For example, when forming the metal-doped diamond layer by the above-mentioned hot filament CVD method, a gas serving as a carbon source (e.g., methane) and a gas serving as a phosphorus source (phosphine (PH 3 By making the metal-doped diamond layer contain the element phosphorus, the metal-doped diamond layer can contain the element phosphorus. The phosphorus concentration in the metal-doped diamond layer can be, for example, 1×10 18 ~1×10 22 cm -3 in the range of about 1×10 18 ~1×10 21 cm -3 in the range of about 1×10 19 ~1×10 21 cm -3 in the range of about 1×10 20 ~1×10 21 cm -3 The phosphorus concentration in the metal-doped diamond layer is a value measured by secondary ion mass spectrometry (SIMS).

[0027] The crystal structure of the metal-doped diamond layer may be single crystal or polycrystal. For example, if a single crystal substrate is used as the semiconductor substrate on which the metal-doped diamond layer is formed, the single crystal structure is obtained. Also, if a polycrystalline diamond substrate is used, the polycrystalline structure is obtained. Note that, if a heterogeneous substrate (such as a silicon substrate, a silicon carbide substrate, a gallium nitride substrate, an aluminum nitride substrate, a gallium oxide substrate, or an yttria-stabilized zirconia substrate) is used as the semiconductor substrate on which the metal-doped diamond layer is formed, the heterogeneous substrate can be subjected to a so-called "scratching treatment" using diamond fine particles to promote diamond nucleation and grow the metal-doped diamond layer. Note that the scratching treatment may not be necessary depending on the semiconductor substrate.

[0028] From the viewpoint of more suitable exertion of the effect of the present invention, the thickness of metal-doped diamond layer is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more.The preferred range of the thickness of metal-doped diamond layer is about 1-100 μm, about 5-100 μm, about 10-100 μm.Even if the thickness of metal-doped diamond layer is, for example, 100 μm or less, it can sufficiently exert the effect of suppressing the defect of semiconductor substrate from being inherited by active layer, etc., and the thinner the thickness of metal-doped diamond layer, the more it can suppress the defect of metal-doped diamond layer itself from becoming large.

[0029] The area ratio of one side of the metal-doped diamond layer is preferably 60% or more, more preferably 80% or more, and even more preferably 95% or more, relative to the area ratio of one side of the semiconductor substrate being 100%, and may be 100%.

[0030] In addition, from the viewpoint of more favorably exerting the effect of the present invention, it is preferable that the metal-doped diamond layer is formed on the surface of the semiconductor substrate (the semiconductor substrate and the metal-doped diamond layer are in contact with each other).That is, it is preferable to form the metal-doped diamond layer on the surface of the semiconductor substrate by hot filament CVD method.By forming the metal-doped diamond layer on the surface of the semiconductor substrate, the defects caused by the structure of the semiconductor substrate are not easily inherited by the active layer stacked on the metal-doped diamond layer, and the deterioration of the diode characteristics due to the increase in the area of ​​the diode can be favorably suppressed.

[0031] An example of a method for producing a metal-doped diamond layer by hot filament CVD includes the following steps. Step (1): A step of introducing a carrier gas containing a carbon source and, if necessary, an impurity source (e.g., a boron source, a phosphorus source, etc.) into a vacuum chamber in which a semiconductor substrate and a filament are placed. Step (2): A deposition step in which a carrier gas containing a carbon source is heated by a filament to deposit a film of a diamond containing a metal on a semiconductor substrate.

[0032] In step (1), the metal constituting the filament placed in the vacuum vessel is not particularly limited as long as it can form a filament. Specific examples of the metal element include tungsten, tantalum, rhenium, ruthenium, etc., and among these, tungsten is preferred. The metal element may be used alone or in combination of two or more kinds.

[0033] In step (1), the semiconductor substrate placed in the vacuum chamber is the semiconductor substrate described above.

[0034] In step (1), after the vacuum vessel is evacuated, a carrier gas containing a carbon source is introduced. The carbon source is not particularly limited as long as it can form diamond, and for example, methane and the like can be mentioned. The carbon source may be used alone or in combination of two or more. In addition, when doping boron as an impurity, the boron source is not particularly limited as long as it can be doped into diamond as boron and can maintain the crystal structure of diamond, and preferably includes trimethylboron, diborane and the like. The impurity source may be used alone or in combination of two or more.

[0035] The carrier gas is not particularly limited, and for example, hydrogen gas can be used. The concentration of the carbon source in the carrier gas containing the carbon source is preferably about 0.5 to 5.0% by volume, more preferably about 1.0 to 3.0% by volume.

[0036] In addition, when the metal-doped diamond layer contains impurities, the concentration of the impurity source relative to the carbon source in the carrier gas may be appropriately set according to the concentration of the impurity contained in the metal-doped diamond layer. For example, when boron is contained as an impurity, the concentration of boron in the metal-doped diamond layer may be set to 1×10 18 cm -3 ~1×10 21 cm -3 In this case, the concentration of the boron source relative to the carbon source in the carrier gas is preferably 100 ppm or more, more preferably about 1000 to 20000 ppm, and even more preferably about 5000 to 10000 ppm.

[0037] In step (2), a film-forming step is carried out by heating the carrier gas with a filament to form a metal-doped diamond layer on a semiconductor substrate.The heating temperature of the filament can be appropriately set according to the type of metal element that constitutes the filament used and the concentration of metal element and impurity that are contained in the metal-doped diamond layer, and is preferably about 2000 to 2400°C, more preferably about 2000 to 2200°C.

[0038] The total pressure in the vacuum vessel in step (2) is not particularly limited, and may be, for example, about 10 to 100 Torr, and more preferably about 10 to 80 Torr.

[0039] The temperature of the semiconductor substrate in step (2) is not particularly limited, and may be, for example, about 700 to 1100°C, more preferably about 700 to 900°C.

[0040] The film formation time in step (2) may be appropriately selected depending on the desired thickness, etc., and is usually about 3 to 50 hours.

[0041] (active layer) In the nuclear battery of the present invention, an active layer is laminated on the metal-doped diamond layer (opposite side to the semiconductor substrate). The material for forming the active layer is not particularly limited, as long as it does not impair the effect of the present invention. Since diamond is used in the nuclear battery of the present invention, the active layer can be suitably formed, for example, by impurity-doped diamond. In addition, when the active layer is formed by a material other than impurity-doped diamond, the active layer can also be formed by, for example, silicon, silicon carbide, gallium nitride, gallium oxide, etc.

[0042] In the present invention, when the active layer is formed by impurity-doped diamond, the impurities in the impurity-doped diamond include boron, phosphorus, etc. As with the above-mentioned metal-doped diamond layer, when the impurity-doped diamond is made to be a p-type semiconductor, the impurity-doped diamond contains impurities such as boron, and when the impurity-doped diamond is made to be an n-type semiconductor, the impurity-doped diamond contains impurities such as phosphorus. The impurity concentration in the impurity-doped diamond is, for example, 1×10 18 ~1×10 22 cm -3 in the range of about 1×10 18 ~1×10 21 cm -3 in the range of about 1×10 19 ~1×10 21 cm -3 in the range of about 1×10 20 ~1×10 21 cm -3 The impurity concentration in the impurity-doped diamond layer is a value measured by secondary ion mass spectrometry (SIMS).

[0043] When the metal-doped diamond layer is an n-type semiconductor, the active layer is a p-type semiconductor, and when the metal-doped diamond layer is a p-type semiconductor, the active layer is an n-type semiconductor.In addition, the active layer may be formed on the surface of the metal-doped diamond layer (i.e., the metal-doped diamond layer and the active layer may be in direct contact), or the metal-doped diamond layer and the active layer may be laminated via an intrinsic semiconductor layer or the like (see Fig. 15 to Fig. 17).

[0044] In addition, the active layer is a layer different from the metal-doped diamond layer. Therefore, the active layer is not doped with metal. When forming the active layer with impurity-doped diamond, if the hot filament CVD method is used, the metal element in the metal filament is included in the impurity-doped diamond, so that the formation of the impurity-doped diamond is preferably performed by, for example, the microwave CVD method, which can form the impurity-doped diamond without containing the metal element. The formation method of the impurity-doped diamond film using the microwave CVD method can adopt a known method.

[0045] The thickness of the active layer can be appropriately set depending on the size of the nuclear battery, and is, for example, about 10 to 200 μm, preferably about 10 to 50 μm.

[0046] The area ratio of one side of the active layer is preferably 60% or more, more preferably 95% or more, and may be 100%, relative to the area ratio of one side of the semiconductor substrate, which is 100%.

[0047] (Radioactive material containing layer) In the nuclear battery of the present invention, the electrode for extracting the electromotive force generated by emitting radiation to the radioactive substance-containing layer has a structure (diode structure) electrically connected to a laminate including a semiconductor substrate, a metal-doped diamond layer, an active layer, and a radioactive substance-containing layer in this order.The radioactive substance-containing layer is laminated at least on the active layer, and the active layer is irradiated with radiation.A radioactive substance-containing layer may be further provided on the semiconductor substrate side.

[0048] The radioactive material-containing layer may be a known layer used in nuclear batteries.

[0049] The radioactive material-containing layer is a layer containing a radioactive material that emits at least one of α-rays, β-rays, γ-rays, x-rays, neutron rays, etc. Specific examples of the radioactive material-containing layer include layers containing radioactive isotopes such as Cm-244, Am-241, Po-210, and Pu-238 (which emit α-rays), radioactive isotopes such as Ni-63 and H-3 (which emit β-rays), radioactive isotopes such as Cf-252 (which emit neutron rays), and radioactive isotopes such as Fe-55, Co-60, and Cs-137 (which emit γ-rays and x-rays) (see MG Spensor et al., Appl., Phys., Rev. 6 031305 (2019) and MA Prelas, Progress in Nuclear Energy 75 (2014) 117-148., etc.).

[0050] The area of ​​one side of the radioactive substance-containing layer is preferably 60% or more, more preferably 95% or more, and may be 100%, relative to the area of ​​one side of the semiconductor substrate, which is taken as 100%.

[0051] The thickness of the radioactive substance-containing layer can be appropriately set depending on the size of the nuclear battery, and is, for example, about 10 to 500 μm, and preferably about 10 to 50 μm.

[0052] (electrode) In the nuclear battery of the present invention, the electrodes are electrically connected to a laminate having a semiconductor substrate, a metal-doped diamond layer, an active layer, and a radioactive substance-containing layer in this order. Specifically, one of the pair of electrodes is formed on a part of the surface of the active layer, and the other electrode is formed on the surface of the semiconductor substrate, the surface of the metal-doped diamond layer, etc.

[0053] The electrodes may be any known electrodes used in nuclear batteries.

[0054] The electrodes can be formed, for example, by a metal vapor deposition film. Examples of metals constituting the electrodes include molybdenum, titanium, gold, ruthenium, aluminum, and platinum.

[0055] The area of ​​one side of the electrode is preferably 60% or more, more preferably 95% or more, and may be 100%, relative to the area of ​​one side of the semiconductor substrate, which is taken as 100%.

[0056] The thickness of the electrode can be appropriately set depending on the size of the nuclear battery, and is, for example, about 10 to 200 nm, and preferably about 30 to 100 nm.

[0057] (Diode structure) As mentioned above, one of the features of the nuclear battery of the present invention is that a metal-doped diamond layer is provided between a semiconductor substrate and an active layer.Therefore, when forming a laminate by stacking each layer including an active layer on a semiconductor substrate by vapor deposition, defects are unlikely to be formed in the active layer, and it is considered that the deterioration of the diode characteristics associated with the increase in the area of ​​the diode is suppressed.That is, by arranging a metal-doped diamond layer, which was not provided in the conventional technology, between a semiconductor substrate and an active layer, compared with the case where an active layer is stacked on a semiconductor substrate, the defects caused by the structure of the semiconductor substrate are unlikely to be inherited by the active layer, and as a result, defects are unlikely to be formed in the active layer, and it is considered that the deterioration of the diode characteristics associated with the increase in the area of ​​the diode is suppressed.

[0058] In the nuclear battery of the present invention, except that the diode structure is provided with a metal-doped diamond layer between a semiconductor substrate and an active layer, the structure of a conventional nuclear battery using diamond can be applied. Figures 6 to 17 show schematic examples of the diode structure applied to the nuclear battery of the present invention.

[0059] Figure 6 shows a Schottky barrier diode structure in which a semiconductor substrate (insulating) / metal-doped diamond layer (p-type) / active layer / radioactive substance-containing layer are stacked in this order, with a Schottky electrode formed on the surface of the active layer and an ohmic electrode formed on the surface of the metal-doped diamond layer (p-type).

[0060] Figure 7 shows a Schottky barrier diode structure in which a semiconductor substrate (insulating) / metal-doped diamond layer (n-type) / active layer / radioactive substance-containing layer are stacked in this order, with a Schottky electrode formed on the surface of the active layer and an ohmic electrode formed on the surface of the metal-doped diamond layer (n-type).

[0061] Figure 8 shows a Schottky barrier diode structure in which a radioactive substance-containing layer / semiconductor substrate (p-type conductivity) / metal-doped diamond layer (p-type) / active layer / radioactive substance-containing layer are stacked in this order, with a Schottky electrode formed on the surface of the active layer and an ohmic electrode formed on the surface of the semiconductor substrate (p-type conductivity).

[0062] Figure 9 shows a Schottky barrier diode structure in which a radioactive substance-containing layer / semiconductor substrate (n-type conductivity) / metal-doped diamond layer (n-type) / active layer / radioactive substance-containing layer are stacked in this order, with a Schottky electrode formed on the surface of the active layer and an ohmic electrode formed on the surface of the semiconductor substrate (n-type conductivity).

[0063] Figure 10 shows a pn junction diode structure in which a semiconductor substrate (insulating) / metal-doped diamond layer (p-type) / active layer (n-type) / radioactive substance-containing layer are stacked in this order, with an electrode formed on the surface of the active layer and an ohmic electrode formed on the surface of the metal-doped diamond layer (p-type).

[0064] Figure 11 shows a pn junction diode structure in which a semiconductor substrate (insulating) / metal-doped diamond layer (n-type) / active layer (p-type) / radioactive substance-containing layer are stacked in this order, with an electrode formed on the surface of the active layer and an ohmic electrode formed on the surface of the metal-doped diamond layer (n-type).

[0065] Figure 12 shows a pn junction diode structure in which a radioactive substance-containing layer / semiconductor substrate (p-type conductivity) / metal-doped diamond layer (p-type) / active layer (n-type) / radioactive substance-containing layer are stacked in this order, with an electrode formed on the surface of the active layer (n-type) and an ohmic electrode formed on the surface of the semiconductor substrate (p-type conductivity).

[0066] Figure 13 shows a pn junction diode structure in which a radioactive substance-containing layer / semiconductor substrate (n-type conductivity) / metal-doped diamond layer (n-type) / active layer (p-type) / radioactive substance-containing layer are stacked in this order, with an electrode formed on the surface of the active layer (p-type) and an ohmic electrode formed on the surface of the semiconductor substrate (n-type conductivity).

[0067] Figure 14 shows a pin junction diode structure in which a semiconductor substrate (insulating), a metal-doped diamond layer (p-type), an intrinsic semiconductor layer (i-type), an active layer (n-type), and a radioactive substance-containing layer are stacked in this order, with an electrode formed on the surface of the active layer (n-type) and an ohmic electrode formed on the surface of the metal-doped diamond layer (p-type).

[0068] Figure 15 shows a pin junction diode structure in which a semiconductor substrate (insulating) / metal-doped diamond layer (n-type) / intrinsic semiconductor layer (i-type) / active layer (p-type) / radioactive substance-containing layer are stacked in this order, with an electrode formed on the surface of the active layer (p-type) and an ohmic electrode formed on the surface of the metal-doped diamond layer (n-type).

[0069] FIG. 16 shows a pin junction diode structure in which a radioactive substance-containing layer / semiconductor substrate (p-type conductivity) / metal-doped diamond layer (p-type) / intrinsic semiconductor layer (i-type) / active layer (n-type) / radioactive substance-containing layer are stacked in this order, with an electrode formed on the surface of the active layer (n-type) and an ohmic electrode formed on the surface of the semiconductor substrate (p-type conductivity).

[0070] Figure 17 shows a pin junction diode structure in which a radioactive substance-containing layer / semiconductor substrate (n-type conductivity) / metal-doped diamond layer (n-type) / intrinsic semiconductor layer (i-type) / active layer (p-type) / radioactive substance-containing layer are stacked in this order, with an electrode formed on the surface of the active layer (p-type) and an ohmic electrode formed on the surface of the semiconductor substrate (n-type conductivity). EXAMPLES

[0071] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the examples.

[0072] <Example 1> A single crystal diamond substrate (100) with a size of 3 mm square and a thickness of 500 μm was prepared as a semiconductor substrate. Next, a single crystal diamond was deposited on the surface of the semiconductor substrate as a metal-doped diamond layer by hot filament chemical vapor deposition (hot filament CVD). The deposition conditions were as follows:

[0073] (Conditions for forming metal-doped single crystal diamond films) Carrier gas: 97% hydrogen by volume, 3% methane by volume (carbon source), and the volume concentration of trimethylboron (boron source) relative to methane (in the gas phase [B / C] gas , ppm): 6500 ppm Total pressure: 10 Torr Filament material: 99.9% pure tungsten Filament temperature: 2000~2200℃ ·Substrate temperature: 800℃ Film production time: 10 hours Film thickness: 4μm Offset angle of substrate pretreatment: 2.5°

[0074] (Measurement of metal and boron concentrations in metal-doped diamond layers) The metal concentration (tungsten concentration) and boron concentration in the metal-doped diamond layer were measured using secondary ion mass spectrometry (SIMS, Cs + The measurement was performed at an ion acceleration voltage of 15.0 kV. As a result, the metal concentration (tungsten concentration) of the metal-doped diamond layer was 2×10 18 cm -3 , boron concentration is 1×10 20 m -3 It was.

[0075] Next, a single crystal diamond film was formed as an active layer (p-layer) on the surface of the metal-doped diamond layer by microwave CVD under the following film formation conditions.

[0076] (Active layer (p-layer) deposition conditions) A boron-doped single crystal diamond film was formed on the surface of a single crystal diamond substrate (100) by microwave CVD under the following film formation conditions. Carrier gas: 96% hydrogen by volume, 4% methane by volume (carbon source) Total pressure: 120 Torr ·Substrate temperature: 900℃ Film production time: 3 hours Film thickness: 10μm - Film deposition area: Entire surface of semiconductor substrate Offset angle of substrate pretreatment: 2.5°

[0077] Next, a Schottky electrode (Mo evaporated film, 200 circles with a diameter of 100 μm) was formed on the surface of the active layer, and an Ohmic electrode (Ti evaporated film, 4 circles with a diameter of 300 μm) was formed on the surface of the metal-doped diamond layer, as shown in the schematic diagram of Figure 18, to obtain a Schottky barrier diode (SBD). Note that an Au evaporated film was placed on each electrode as a cap electrode.

[0078] <Comparative Example 1> A single crystal diamond substrate (100) with a size of 3 mm square and a thickness of 500 μm was prepared as a semiconductor substrate. Next, a boron-doped single crystal diamond film was formed on the surface of the semiconductor substrate by microwave CVD. The film formation conditions were as follows.

[0079] (Boron-doped single crystal diamond deposition conditions) Carrier gas: 97% hydrogen by volume, 3% methane by volume (carbon source), and the volume concentration of trimethylboron (boron source) relative to methane (in the gas phase [B / C] gas , ppm) is 10000 volume percent Total pressure: 80 Torr ·Substrate temperature: 1000℃ Board size: 3mm x 3mm Film production time: 10 hours -Thickness of boron-doped single crystal diamond: 1μm Offset angle of substrate pretreatment: 2.5°

[0080] (Measurement of boron concentration in boron-doped single crystal diamond) The metal concentration (tungsten concentration) and boron concentration in boron-doped single crystal diamond were measured using secondary ion mass spectrometry (SIMS, Cs + The measurement was performed at an ion acceleration voltage of 15.0 kV. As a result, the boron concentration of the boron-doped single crystal diamond was 5×10 19 cm -3 It was.

[0081] Next, a single crystal diamond film was formed as an active layer (p-layer) on the surface of the boron-doped single crystal diamond by microwave CVD under the following film formation conditions.

[0082] (Active layer (p-layer) deposition conditions) Carrier gas: 96% hydrogen by volume, 4% methane by volume (carbon source) Total pressure: 120 Torr ·Substrate temperature: 900℃ Film production time: 3 hours Film thickness: 10μm - Film deposition area: Entire surface of semiconductor substrate Offset angle of substrate pretreatment: 2.5°

[0083] Next, a Schottky barrier diode (SBD) was obtained by forming a Schottky electrode (Mo evaporated film) on the surface of the active layer and an ohmic electrode (Ti evaporated film) on the surface of the boron-doped diamond layer using a vacuum deposition method, as shown in the schematic diagram of Figure 19. Note that an Au evaporated film was placed on each electrode as a cap electrode.

[0084] <Example 2> Except for forming one Schottky electrode with a diameter of 700 μm, a Schottky barrier diode (SBD) was obtained in the same manner as in Example 1. The Schottky barrier diode (SBD) of Example 2 has a Schottky electrode area 49 times larger than that of Example 1.

[0085] <Example 3> A Schottky barrier diode (SBD) was obtained in the same manner as in Example 2, except that one Schottky electrode having a diameter of 1000 μm was formed.

[0086] [Evaluation of diode rectification characteristics] The rectification characteristics of the Schottky barrier diodes (electrode diameter 100 μm) obtained in Example 1 and Comparative Example 1 were evaluated by the following method. A graph showing the relationship between the obtained current (A) and voltage (V) is shown in FIG. 1. A semiconductor device analyzer (B1500A, Agilent Technologies) and a microprobe chamber were used for voltage application and current measurement. A probe needle was brought into contact with the electrode of the Schottky barrier diode, the ohmic electrode was grounded, and a voltage was applied to the Schottky electrode. The range and steps of the applied voltage are as follows: Applied voltage: 0~-3.5V (forward), 0~+3.5V (reverse) Step: 0.01V (forward), 0.5V (reverse)

[0087] Similarly, the rectification characteristics were evaluated for the Schottky barrier diode (electrode diameter 700 μm) obtained in Example 2. A graph showing the relationship between the obtained current (A) and voltage (V) is shown in FIG.

[0088] With reference to the method described in S. Maximenko et al., Sci Rep.9 10892 (2019), the Schottky barrier diode obtained in Example 2 was subjected to an electron beam irradiation to perform a characteristic evaluation (characteristic evaluation of a nuclear battery). A graph showing the relationship between current (A) and voltage (V) predicted by calculation is shown in FIG. 3. The evaluation conditions are as follows.

[0089] (Evaluation conditions for characteristics) Radiation source: Ni-63 (extraction efficiency ηβ=13%) Average energy: 17.4keV Radioactivity: 126mCi / cm 2 (~4.66GBq / cm 2 ) Charge collection efficiency of the device is ~100% Average electron-hole pair creation energy ε=13eV Diameter of element: Φ700 μm (diode diameter in Example 2) Short circuit current I sc =0.502nA Open circuit voltage V oc =0.56V Maximum output P mp =0.22nW Form factor FF=0.79 η s =3.39%

[0090] The rectification characteristics of the Schottky barrier diode (electrode diameter 1000 μm) obtained in Example 3 were evaluated in the same manner as in Example 2. A graph showing the relationship between the obtained current (A) and voltage (V) is shown in FIG. As in Example 2, the Schottky barrier diode obtained in Example 3 was subjected to an electron beam irradiation to perform a characteristic evaluation (characteristic evaluation of a nuclear battery) using the method described in S. Maximenko et al., Sci Rep.9 10892 (2019) as a reference. A graph showing the relationship between current (A) and voltage (V) predicted by calculation is shown in FIG. 5. The evaluation conditions are as follows.

[0091] (Evaluation conditions for characteristics) Radiation source: Ni-63 (extraction efficiency ηβ=13%) Average energy: 17.4keV Radioactivity: 126mCi / cm 2 (~4.66GBq / cm 2 ) Charge collection efficiency of the device is ~100% Average electron-hole pair creation energy ε=13eV Diameter of element: Φ1000 μm (diameter of diode in Example 3) Short circuit current I sc =1.03nA Open circuit voltage V oc =0.87V Maximum output P mp =0.74nW Shape factor FF = 0.83 η s =5.55%

Claims

1. A laminate having at least a semiconductor substrate, a metal-doped diamond layer, an active layer, and a radioactive substance-containing layer in this order; an electrode electrically connected to the laminate; Equipped with A nuclear battery, wherein the metal element contained in the metal-doped diamond layer is at least one selected from the group consisting of tungsten, tantalum, rhenium, and ruthenium.

2. 2. The nuclear battery of claim 1, wherein the active layer is formed from impurity-doped diamond.

3. The metal-doped diamond layer has a metal concentration of 1×10 18 cm -3 Above 1 x 10 21 cm -3 3. The nuclear battery according to claim 1 or 2, wherein:

4. The nuclear battery according to any one of claims 1 to 3, wherein the thickness of the metal-doped diamond layer is 1 µm or more and 10 µm or less.

5. The nuclear battery according to any one of claims 1 to 4, wherein the semiconductor substrate is a single crystal diamond substrate, a polycrystalline diamond substrate, a silicon substrate, a silicon carbide substrate, a gallium nitride substrate, an aluminum nitride substrate, a gallium oxide substrate, or an yttria-stabilized zirconia substrate.

6. The nuclear battery according to any one of claims 1 to 5, wherein the metal-doped diamond layer is a p-type semiconductor.

7. 7. The nuclear battery of claim 6, wherein the semiconductor substrate is a p-type semiconductor.

8. 8. The nuclear battery according to claim 6, wherein the active layer is an n-type semiconductor.

9. The nuclear battery according to any one of claims 1 to 5, wherein the metal-doped diamond layer is an n-type semiconductor.

10. 10. The nuclear battery of claim 9, wherein the semiconductor substrate is an n-type semiconductor.

11. 11. The nuclear battery according to claim 9 or 10, wherein the active layer is a p-type semiconductor.

12. The nuclear battery according to any one of claims 1 to 11, wherein the metal-doped diamond layer and the active layer are in direct contact.

13. The nuclear battery according to any one of claims 1 to 11, further comprising an intrinsic semiconductor layer between the metal-doped diamond layer and the active layer.

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