JP6519103B2 - Light emitting structure and thermophotovoltaic power generation system using the same, visible light lighting device, gas detection device - Google Patents

Description

  The present invention relates to a light emitting structure, and more particularly to a light emitting structure that can be used as a near infrared light emitter for thermal photovoltaic power generation, a filament for visible light illumination, a mid infrared light source for gas detection, and the like.

  When an emitter made of a material such as refractory metal or ceramic is heated to a temperature of 1000 ° C. or more, a strong infrared ray is obtained. In thermo-photo-voltaic power generation (hereinafter referred to as TPV), infrared light emitted from the emitter is received by a photoelectric conversion element called a PV (photo-voltaic) cell and converted into electricity for power generation Do. Non-Patent Document 1 introduces thermal photovoltaic power generation under the title “Application of Thermal Radiation Spectrum Control Technology to Thermal Photovoltaic Power Generation”. Thermophotovoltaic power generation can use various heat sources, and can use not only sunlight but also liquid or gaseous fuel. Thermophotovoltaic power generation may be widely used in the future because it is quieter and easier to transport than mechanical engine power generation. However, while the power generation efficiency of about 15% is obtained in the small mechanical engine power generation, the efficiency of the thermal photovoltaic power generation of Non-Patent Document 2 is only about 12%. In order to spread thermal photovoltaic power generation in the future, it is necessary to improve efficiency and output. Therefore, development of high output and high efficiency emitters is expected.

  According to Stefan-Boltzmann's law, it is known that the light intensity per unit area emitted from an object is proportional to the fourth power of the temperature of the object. Therefore, to raise the power generation output, it is effective to raise the temperature of the emitter.

  It is the black body that the radiant energy is the largest. Due to Plank's law, the wavelength spectrum of black body radiation is determined solely by temperature. The wavelength spectrum of black body radiation has a wavelength width of several μm and has a long tail on the long wavelength side. According to Wien's law, the peak wavelength λB of blackbody radiation at temperature T (K) is given by 2900 / T. For example, in the case of 1400 K, λB = 2.07 μm. The radiation intensity in the wavelength band of 1.4 μm or less is small. Since there is a limit to the temperature that the emitter can withstand, a PV element with a sensitivity band of 1.5 μm to 2.5 μm is usually used for TPV. Non-Patent Document 3 is a report of a PV cell using a GaSb material, and a photoelectric conversion efficiency of 30% or more is reported. FIG. 36 shows the wavelength dependence of the external quantum efficiency of GaSb-PV elements having different P doping shapes described in Non-Patent Document 3. The GaSb-PV element has a sensitivity band at a wavelength of 0.6 μm to 1.8 μm, and has high photoelectric conversion efficiency at a wavelength band of 1.5 μm to 1.7 μm. The room temperature band gap wavelength of the GaSb crystal is 1.7 μm, but the light reception limit wavelength is increased to 1.8 μm by doping to GaSb. In order to enhance the efficiency of thermal photovoltaic power generation, it is necessary to control the emission spectrum of the emitter in a wavelength band in which the PV device can generate power.

  To control the emission spectrum, the emissivity of the emitter must be controlled. Emissivity is a value obtained by dividing the radiation intensity from a heated object by the radiation intensity of a black body at the same temperature, and depends on the wavelength. According to Kirchhoff's law, emissivity and absorptivity are equal at local thermal equilibrium. In the case of an opaque object such as metal, the transmittance is zero, so the sum of reflectance and absorptivity is 1. Therefore, in the case of an object such as metal, an emissivity spectrum can be obtained if a reflectance spectrum at a certain temperature can be obtained. The emission spectrum is obtained by multiplying the emissivity spectrum by the black body emission spectrum.

  In order to obtain high conversion efficiency, the peak wavelength of the thermal emission spectrum from the emitter is controlled to a wavelength band of 1.5 μm to 1.7 μm (in the case of GaSb-PV cell) where the light receiving sensitivity of the PV device is high, and the peak wavelength It is desirable to make the emissivity at as close to 1 as possible, and to make the wavelength spectrum width as small as possible.

  Since it is advantageous for the emitter temperature to be high in order to obtain a high output, a refractory metal such as tungsten (element symbol W) resistant to high temperatures of 1000 ° C. or higher has been used as the emitter material. However, when a flat plate of tungsten is used as the emitter, there is a problem that the emissivity of light is small and the peak wavelength of the spectrum can not be controlled. In addition, since the light emission spectrum has a long-tailed shape in a wavelength region of 1 μm or more, there is a problem that high conversion efficiency can not be obtained. When the emitter has a high temperature and a strong radiation intensity, and the wavelength spectrum width is wide, the long wavelength component which the PV cell can not receive is absorbed to raise the temperature of the cell, and the photoelectric conversion efficiency is significantly reduced.

  Non-Patent Document 4 is entitled “The present status of TPV power generation system and selective emitter material technology”, and introduces thermal photovoltaic power generation and wavelength selective emitter technology used therefor. The wavelength selective emitter is an emitter whose emission spectrum is narrower than the black body. An oxide emitter comprising a rare earth element such as Yb or Er described therein has a narrow emission spectrum. However, the peak wavelength is fixed to the emission wavelength of 1.1 μm of Yb or 1.5 μm of Er, and there is a problem that the conversion wavelength does not match the existing GaSb-PV cell. In addition, in order to cause 1.1 μm of Yb to emit light strongly, it is necessary to raise the emitter temperature to 1700 ° C. or higher, which makes it difficult to control the reliability of the emitter and the heat radiation of the device. When the emitter temperature is lowered, the light emission intensity in the 1.1 μm band becomes extremely small, and there is a problem that a practical output can not be obtained.

  The first solution to solve such a problem is to reflect infrared light of a wavelength that can not be generated by the PV cell by an optical filter and return it to the emitter. However, it is not easy to produce a heat-resistant filter that reflects only infrared light ranging from a wide wavelength range of 1.8 μm to 10 μm or more and can be placed beside a high temperature emitter.

  The second solution is a method of forming an oxide film or a semiconductor layer on the surface of tungsten. Patent Document 1 "Infrared Light Source" describes that a MgO + W cermet layer 902 is formed on the surface of a tungsten flat plate as a technique for preventing oxidation of tungsten. However, the cermet layer 902 is an oxide film that protects W and transmits light. In addition, controlling the film thickness of the cermet film 902 to improve the emissivity is also not described.

  Further, in Patent Document 2 “Antireflection film and emitter for thermal photovoltaic power generation”, a β-FeSi semiconductor layer having a refractive index of 4 or more is formed on an Fe substrate on the surface of a tungsten flat plate, and is further reflected on the metal surface. By adjusting the refractive index and the film thickness of the thin film so that the phase of the light is reversed to the phase of the light reflected by the thin film surface, it is possible to prevent the reflection on the emitter surface. (Paragraph 0012, FIG. 1).

  However, in this document, it is necessary to select a material having an appropriate refractive index and to adjust the film thickness so as to perform phase inversion.

JP, 2011-222211, A JP, 2011-96770, A Patent No. 3472838 JP 2005-276556 A Re-issued patent WO2005 / 091335 Unexamined-Japanese-Patent No. 2007-234362 JP, 2013-131467, A

Applied Physics 73: 7 P 952 (2004) Fraas, L. M .; Avery, J. E .; Minkin, L .; Huang, H. X., Photovoltaic Specialists Conference (PVSC), 2011 37th IEEE, Page: 002050-002055 JX Crystal, Inc. O. V. Sulima, A. W. Bett / Solar Energy Materials & Solar Cells 66 (2001) 533-540 Applied Physics Vol. 76, No. 3 P 281 (2007) Hitoshi Sai and Hiroo Yugami, Appl. Phys. Lett., Vol. 85, No. 16, 18 October 2004 p3399 [1 "Thermophotovoltaic generation with selective radiators based on tungsten surface gratings" "wavelength selective radiation based on tungsten surface gratings Associated photovoltaic photovoltaic generation " MU Pralle, et. Al. Appl. Phys. Lett., Vol. 81, No. 25, 16 December 2002 P4685 "Photonic crystal enhanced narrow-band infrared emitters" Metal cover in Si hole-"Photo crystal enhanced narrow band red Outer emitter "

  The third solution in controlling the emission spectrum of the emitter is the method described in the article "Thermal Photovoltaic Power Generation with Wavelength Selective Radiation Based on Tungsten Surface Grating", NPL 5 This is a method of narrowing the radiation spectrum by forming a light emitting structure in which a large number of rectangular micropores are arranged at intervals of about 1 μm in a tungsten flat plate. In this Non-Patent Document 5, this light emitting structure is called a tungsten surface diffraction grating. Patent Document 3 "Wavelength-Selective Sunlight Absorbent Material and Method of Manufacturing the Same" describes a method of using a tungsten surface diffraction grating as a solar light absorbing material and a method of manufacturing the same. Their contents are also introduced to Non-Patent Document 1 in an easy-to-understand manner.

  FIG. 37 shows the appearance and the cross section of the surface portion of the tungsten surface diffraction grating of Non-Patent Document 5. As shown in FIG. In the tungsten surface diffraction grating, rectangular fine holes 2 are periodically formed in a single crystal tungsten 1 in a square lattice shape. When the surface diffraction grating is irradiated with light, light having a wavelength shorter than the wavelength λ0 is absorbed inside the fine holes, and light having a wavelength longer than the wavelength λ0 is reflected. According to Kirchhoff's law, when the surface diffraction grating is heated, light having a wavelength shorter than the wavelength λ0 is emitted, and emission of light having a wavelength longer than the wavelength λ0 is suppressed. This narrows the wavelength spectrum due to the metal microcavity effect on electromagnetic waves. As a result, the peak wavelength of the radiation spectrum can be controlled to increase the peak intensity and at the same time narrow the wavelength width. Although Non-Patent Document 5 describes tungsten and molybdenum as materials of surface diffraction gratings, there is no description of other materials.

  FIG. 38 shows a thermal emissivity spectrum at 1400 K from a surface diffraction grating having three different structures formed on a tungsten substrate described in Non-Patent Document 1. As shown in FIG. The scanning electron micrograph of the sample is inserted in the figure. Assuming that the period of the fine holes 2 is Λ, the length of one side of the square opening is a, and the depth of the holes is d, when a / 1〜2 is 0.7 to 0.8 and d / a is 1, the wavelength is 1 to 2 μm It is stated that the thermal emissivity of

  However, sufficient spectral narrowing has not been obtained using tungsten grating emitters. The emissivity is as high as 0.4 at a wavelength of 2 μm, and even at a wavelength of 4 μm or more, a tailing with an emissivity of 0.2 or more is observed. In particular, the 2 μm to 4 μm wavelength region of the radiation spectrum is a strong region of about 1000 ° C. of black body radiation, and in order to realize high conversion efficiency, the intensity of the radiation spectrum in this wavelength region must be reduced as much as possible.

  Patent Document 5 (republished patent WO 2005/091335) is a radiator that converts heat into electromagnetic waves and radiates from the surface, and a plurality of microcavities are formed in at least a partial region of the surface; It is described that the surface of No. 2 is formed of a layer containing tungsten (tungsten carbide) bonded to carbon. However, tungsten carbide has a low emissivity and is not suitable for narrowing the emission spectrum from the emitter.

Further, in Patent Document 6 (Japanese Patent Application Laid-Open No. 2007-234362), an incandescent lamp having a plurality of microcavity structures on its surface, the microcavity is a filament base made of a high melting point material and the same high melting point material on the surface. The ones with a worn structure are described. The adherend is formed with a thin film of the same or different quality as the substrate. [0014] The paragraph "It is preferable to use the same high-melting point material of the same quality as the filament substrate and the adherend, but it is possible to use high-melting point materials of different materials if desired." The adherend is for narrowing the opening of the microcavity, and it is not necessary for the substrate and adherend to be different materials, and examples of different materials are not shown.

  Furthermore, according to Patent Document 7 (Japanese Patent Application Laid-Open No. 2013-131467), an incandescent lamp is coated with a substrate of a first metal material (eg, tungsten) and a second metal material (eg, tantalum) having a melting point lower than that of the substrate. It is described. In the present invention, in order to obtain a filament with high conversion efficiency from electric power to visible light, high energy visible light is emitted by bremsstrahlung of a metal film having a melting point lower than that of the substrate. In Patent Document 7, the microcavity structure is not formed.

  In this patent document (0022), “in the present invention, by covering the substrate with a metal film composed of a metal material having a melting point lower than that of the substrate, a metal film having a low melting point is obtained at the same temperature as the substrate. "Making it close to a softened state (melted state or liquid state)." Therefore, when the present invention is applied to a microcavity structure, the second metal material becomes molten or liquid at high temperature to block the microcavity, and wavelength selectivity can not be obtained. It is also conceivable that, after the vaporized second metal material adheres to the inner surface of the bulb, it detaches again and adheres to the microcavity to close the microcavity.

  An object of the present invention is to provide a light emitting structure capable of narrowing the wavelength spectrum width of a thermal radiation spectrum and improving the efficiency and output of thermal photovoltaic power generation.

  The present invention is a light emitting structure having a plurality of micropores, wherein the micropores comprise a first material containing a first metal element, and at least a portion of the surface other than the micropores is provided with the first material. A second material containing a second metal element different from the metal element of the first metal element, and the emissivity of the first material is the light of a wavelength larger than the peak wavelength of the thermal radiation spectrum emitted by the light emitting structure It is a light emitting structure characterized by being larger than the emissivity of the material of 2.

  According to the present invention, it is possible to provide a light emitting structure capable of narrowing the wavelength spectrum width of the thermal radiation spectrum and improving the efficiency and output of thermal photovoltaic power generation.

It is a figure which shows the external appearance of the surface part of the light emission structure which is 1st Example of this invention, and its cross section. BRIEF DESCRIPTION OF THE DRAWINGS It is a perspective view explaining the TPV electric power generation system of 1st Example of this invention. It is sectional drawing of the emitter part of 1st Example of this invention. It is a figure which shows a thermal radiation spectrum when the light-emitting structure of 1st Example of this invention is heated to 1400K. Iritsu spectrum release of W flat and Ta flat is a diagram showing a. It is 1st explanatory drawing of the manufacturing process of the emitter of this invention. It is 2nd explanatory drawing of the manufacturing process of the emitter of this invention. It is 3rd explanatory drawing of the manufacturing process of the emitter of this invention. It is 4th explanatory drawing of the manufacturing process of the emitter of this invention. It is 5th explanatory drawing of the manufacturing process of the emitter of this invention. It is 6th explanatory drawing of the processing process of the emitter of this invention. It is a figure which shows the external appearance of the surface part of the light emission structure which is the 2nd Example of this invention, and its cross section. It is a figure which shows the external appearance of the TPV electric power generating apparatus of the 2nd Example of this invention. It is sectional drawing of the TPV electric power generating apparatus of the 2nd Example of this invention. It is a top view of the TPV electric power generating apparatus of 2nd Example of this invention. It is a figure which shows the cross section of the emitter junction part of 2nd Example of this invention. It is a figure which shows the emissivity spectrum of the flat plate of Ta and Cr. It is a figure which shows the thermal radiation spectrum (1400K) of the light emission structure of the 2nd Example of this invention. It is a figure which shows the light emission structure of 3rd Example of this invention. It is a figure which shows the emissivity spectrum of the flat plate of Cr, Zr, V, W. FIG. It is a figure which shows the emissivity spectrum of the flat plate of W, Mo, Nb, and Ta. It is an Elingham chart of the oxide used for this invention. It is a figure which shows the light emission structure of the 4th Example of this invention. It is a figure which shows the light emission structure of the 5th Example of this invention. It is explanatory drawing of the manufacturing process of the light emission structure of the 5th Example of this invention. It is a figure which shows the light emission structure of the 6th Example of this invention. It is a figure which shows the light emission structure of the 7th Example of this invention. Figure 8 shows a light emitting structure according to an eighth embodiment of the invention; It is sectional drawing of the infrared gas detector of the 8th Example of this invention. It is a figure which shows the thermal radiation spectrum (600 K) of the light emission structure of the 8th Example of this invention. FIG. 10 is a view showing a light emitting structure according to a ninth embodiment of the present invention. It is sectional drawing of the incandescent lamp of 9th Example of this invention. It is a figure which shows the thermal radiation spectrum (2500 degreeC) of the light emission structure of the 9th Example of this invention. It is a figure explaining the material of 9 types of Examples of a nonpatent literature 5 and the light emission structure of this invention, a structure, and use. FIG. 7 shows the materials and structure of another embodiment of the light emitting structure of the present invention. It is a figure which shows the wavelength dependence of the external quantum efficiency of GaSb-PV element from which P doping shape differs. It is a figure which shows the external appearance and the cross section of the surface part of the tungsten surface diffraction grating of a nonpatent literature 5. FIG. FIG. 7 is a thermal emissivity spectrum at 1400 K from a surface grating having three different structures formed on a tungsten substrate. It is a figure which shows the emissivity spectrum of Cr, Zr, V, W flat plate.

Embodiments of the present invention will be described in detail below with reference to the drawings.
First Embodiment
[Description of structure]
The light emitting structure according to the first embodiment of the present invention is a plate having a length of 5 cm, a width of 2 cm, and a thickness of 6 mm, and micropores are periodically formed on the surface in a square lattice shape. FIG. 1 shows the appearance of the surface portion of the light emitting structure according to the present embodiment and the cross section thereof.

  The light emitting structure 11 of the first embodiment comprises a light emitting structure 12 of single crystal tungsten and a tantalum cap layer 13 formed on the surface thereof, and micropores 14 are periodically formed on the surface. The thickness t_cap of the cap layer is 0.30 μm. The period の 15 of the micropores is 0.96 μm. The aperture shape of the fine holes 14 is a square, and the length L16 of one side of the square is 0.8 μm, and the depth t of the holes is 1.42 μm. The Λ / L ratio (= 0.96 / 0.8) is 1.2, and the t / L ratio (= 1.42 / 0.8) is 1.78. The t_cap / t ratio (= 0.30 / 1.42) is 0.21.

  By adding 5 w% of Re (rhenium) to the W body, the ductility is increased and it becomes easy to process. Alternatively, when polycrystalline W is used as the main body, the addition of K (potassium), Si, or Al, La, Ce oxides to W raises the recrystallization temperature, thereby increasing the shape stability at high temperatures. . It is preferable to use a high melting point material having a melting point of 1000 ° C. or more as the material of the light emitting structure and the cap layer of the light emitting structure of the present embodiment.

  FIG. 2 is a perspective view showing the TPV power generation system of the first embodiment. The TPV power generation system of the first embodiment includes a support base 71, a gas introduction pipe 72, a gas burner 73, a flame port 74, a light emitting structure (right) 75, a spacer 76, a light emitting structure (left) 77, The heat insulating support 78, the minute hole array 79, the support plate 80, the PV element 81, the heat dissipation plate 82, the support plate 83, the PV element 84, and the heat dissipation plate 85 are provided.

  A gas introduction pipe 72 is erected and penetrated on a support 71, and a gas burner 73 is provided thereon. A flame port 74 is opened at the upper end of the gas burner 73. A light emitting structure (left) 77 and a light emitting structure (right) 75 are supported by a pair of heat insulating supports 78 above the flame port 74 so that the micropore array 79 is in the opposite direction. The light emitting structures 75, 77 are spaced apart by two spacers 76. Furthermore, the heat sinks 82 and 85 provided with the PV elements 81 and 84 are supported by the support plates 80 and 83 at positions facing the minute hole array 79 of the light emission structures 75 and 77.

  The two PV elements 81 and 84 are both GaSb-based photoelectric conversion elements. The heat sinks 82 and 85 use a heat sink obtained by processing a copper or aluminum material into a concavo-convex shape. The light emitting structure (right) 75 and the light emitting structure (left) 77 are the light emitting structures of the first embodiment. The method of joining the light emitting structure and the spacer 76 may be a welding method, but the inset method was used.

  FIG. 3 shows a cross-sectional view of the emitter portion of the first embodiment. The light emitting structures (right) 75 and 76 are joined back-to-back with a bonding joint 86 via a spacer 76 with the forming surface of the micropore array 79 on the outside. This is a method of cutting the parts to be joined together and joining them by male and female fitting. The heat insulating support 78 is a heat-resistant ceramic with low thermal conductivity and supports the emitter. The heat insulating support 78 is joined to the spacer 76 by a fitting joint 87 by means of a bar-like projection coming out of the spacer 76. The spacer 76 is the same as the material of the back surface of the light emitting structure.

As shown in FIG. 2, the air and gas introduced by the gas introduction pipe 72 are mixed by the gas burner 73 and burnt by the flame port 74. The ignition means is installed near the flame opening. The combustion temperature can be controlled by the mixing ratio of air and gas. The gas burner 73 can heat the back surfaces of the light emitting structures 75 and 77 so that their temperature can be about 1400K. Thus, by the structure which heats only the back surface of a light emission structure, the soot which generate | occur | produced by incomplete combustion adheres to the surface of the light emission structures 75 and 77, and it can prevent filling a micropore array. The near infrared light radiated to both sides from the heated light emitting structures 75 and 77 is received by the PV device 81 and the PV device 84 and converted, and a direct current is taken out to generate power.
[Description of effect]
The heat radiation spectrum when the light emitting structure of the first embodiment is heated to 1400 K is shown by a solid line in FIG. In addition, the thermal emission spectrum of the black body at the same temperature, the thermal emission spectrum of the W light emission structure without the cap layer and the thermal emission spectrum of the Ta light emission structure are shown by a broken line and a dotted line, respectively. The thermal radiation spectrum BB of the black body is a theoretical value. At 1400 K, high wavelength light of energy less than 1 μm is hardly emitted from the black body. When the length L of one side of the square is 0.8 μm, the peak wavelength λp of the emission spectrum is 1.6 μm. The thermal expansion coefficient of W is about 5 × 10 ⁻⁶ (1 / K), and the temperature L of 1000 ° C. increases the length L of one side of the square by about 0.5% due to thermal expansion. The effect on the wavelength is small. The 1 / e full width of the emission spectrum of the W light emitting structure of the Ta cap layer of this example was 0.6 μm. The peak emissivity is approximately one. For tungsten light emitting structures without a cap layer, the 1 / e full width of the spectrum was 0.8 μm. The use of the Ta cap layer reduced the spectral width by 25%. By the way, in the case of a light emitting structure consisting only of Ta without a cap layer, the radiation intensity was halved. In the light emitting structure of this example, the radiation intensity in the region of the photoelectric conversion wavelength of 1.8 μm or more matched that of the light emitting structure of Ta only without the cap layer.

  The spectrum emitted from a light emitting structure heated to a temperature T (600 ° C. ≦ T ≦ 1700 ° C.) when the aperture diameter D of the micropores is about λ0 / 2 with respect to the power generation limit wavelength λ0 of the photoelectric conversion element The peak wavelength λp of the thermal radiation spectrum of the 1 / e value width δ is λ0−δ ≦ λp ≦ λ0. The peak wavelength λp can be set within the effective wavelength range of the photoelectric conversion element by setting the diameter D of the aperture circle of the micropores of the light emitting structure to about half of the desired thermal radiation spectrum peak wavelength λp. The efficiency is highest when the overlap of the light receiving range (λ0−Δ <λ <λ0) of the photoelectric conversion element and the thermal radiation light spectrum is maximized. The spectrum width δ is also somewhat affected by the temperature T.

It shows the Iritsu spectrum release of W flat and Ta flat in FIG. Iritsu release of W flat whereas low in the above wavelength region 2.2 .mu.m, Iritsu release of Ta flat even lower in the above wavelength range 1.4 [mu] m. In the vicinity of the peak wavelength of 1.6 μm, W has a higher emissivity than Ta. In general terms, the emissivity of the first material is greater than the emissivity of the second material at light of a wavelength greater than the peak wavelength of the thermal emission spectrum emitted by the light emitting structure.

  The mechanism of the spectral constriction of the light emission structure of the present Example obtained from the above result is shown. Basically, the microcavity effect of metal to light is used, but the narrowing effect of the wavelength spectrum is enhanced by using W with high emissivity for the main body and Ta with low emissivity for the cap layer. The square aperture width 0.8 μm of the light emitting structure of the present embodiment is half the size of the peak wavelength λp of the radiation spectrum, so light with a wavelength of 1.6 μm or less stands in the space inside the micropores. It can form waves. The standing wave having a wavelength of 1.6 μm or less is well absorbed by tungsten in the vicinity of the surface of the micropore. This means that light with a wavelength of 1.6 μm or less is emitted to the outside from tungsten near the wall surface of the micropore. On the other hand, light having a wavelength of more than 1.6 μm can not form a standing wave in the micropores, so it is not emitted from the micropores to the outside, but emitted from the surface of the Ta cap layer other than the micropores to the outside. As shown in FIG. 5, since the emissivity of tantalum at a wavelength of 1.6 μm or more is lower than that of tungsten, the emission of light with a wavelength of more than 1.6 μm is suppressed. Therefore, in the light emitting structure of the present embodiment, it is considered that the emission spectrum is narrowed because the light near the wavelength of 1.6 μm is strongly emitted and the radiation of the light having the wavelength larger than 1.6 μm is suppressed.

  In order to increase the emissivity, it is desirable that the pores be arranged at a relatively high density. The arrangement of the micropores is easier to create in terms of manufacture, but may not be periodic.

The obtained light intensity is about 1 W / cm 2, which is one digit higher than the light intensity of sunlight. Therefore, the photoelectric conversion efficiency of the PV device is 32% or more. The spectral efficiency of the light emitting structure 75 was 75%. That is, 75% of the light emitted from the light emitting structure 75 at 1400 K was converted to current by the PV element. Therefore, a value of 24% (= 32% x 75%) was obtained as the thermoelectric conversion efficiency of the TPV power generation system of this example. The combustion efficiency at which the gas burner heats the light emitting structure 76 is 65%. Therefore, the power generation efficiency of the TPV power generation system of this example was 15.6%. This corresponds to the power generation efficiency of the mechanical engine. The combustion efficiency is expected to be 83% when a device for preheating the air supplied to the combustion device with the high temperature exhaust gas after combustion is added. In that case, the power generation efficiency of the TPV power generation system is 20%, which exceeds the power generation efficiency of the mechanical engine. In this device the area was 20 cm 2 on both sides, so the light intensity obtained was 20 W. By increasing the area of the light emitting structure 76 and the PV element, the output can be increased as needed.
[Description of manufacturing method]
Although high-melting metals such as Ta have been difficult to use in general vapor deposition, in recent years electron beam vapor deposition and sputtering have been developed, and Ta thin films have become relatively easy to obtain. The sputtering film forming method includes a two-pole sputtering method, a high frequency sputtering method, a magnetron method, a reactive sputtering method and the like, and any of them may be basically used. In the sputtering film formation method, the film formation process is stable, and a dense and strong film can be produced with high accuracy and uniform film thickness. A plurality of metal targets can be used to form an alloy film of a desired composition. In the bipolar sputtering method, a voltage is applied with the target as a cathode and a thin film-forming substrate / substrate as an anode, and gas ion atoms strike the surface of the target, and particles (atoms and molecules) of the target material are ejected onto the substrate. . In the magnetron method, a magnet is placed on the back of the target to generate a magnetic field, gas ion atoms collide with the surface of the target, and secondary electrons ejected are captured by Lorentz force, and ionization of inert gas is performed by cyclotron motion. Facilitate. Since negative ions and secondary electrons can be captured by a magnetic field, the temperature rise of the substrate and substrate can be suppressed, gas ionization can be promoted by the trapped electrons, and the deposition rate can be increased, so the mainstream of deposition techniques by sputtering It has become. The high frequency sputtering method can also form a film other than metal. In reactive sputtering in which a reactive gas such as oxygen or nitrogen is introduced in addition to the Ar gas, an oxide or nitride film can be formed.

  A plate-shaped mirror-polished tungsten single crystal substrate 91 was prepared, and the oxide film on the surface was removed with a sulfuric acid type etchant and an HF type etchant. In a magnetron sputtering apparatus with a back pressure of 1.times.10@-6 Torr, a thin Ta film was deposited to a thickness of 0.3 .mu.m by sputtering on a W crystal substrate at a substrate temperature of 300.degree. The sputtering cathode employed an AC double cathode, and the target used high purity Ta of 145 × 640 × 8 mm t size. The deposition pressure was about 0.15 Pa, the Ar flow rate from the sputtering chamber was 150 sccm, and the Ta sputtering power was 10 kW. The deposition rate was 0.4 μm / min.

  FIG. 6 to FIG. 11 show explanatory views of the processing steps of the emitter of this embodiment. FIG. 6 shows a first explanatory view of the processing step of the emitter of this embodiment. A tantalum thin film 92 is formed on a tungsten single crystal substrate 91, a photoresist 93 is spin coated on the surface of the tantalum thin film 92, an aluminum thin film 94 is deposited thereon using a deposition apparatus, and electron beam exposure is further applied thereon. Resist 95 was spin-coated with a thickness of 0.4 .mu.m and dried. As the photoresist 93, OFRP was used, and as the resist 95 for electron beam exposure, ZEP520A (Nippon Zeon) was used. Instead of the Al thin film 94, a Cr thin film may be used.

  FIG. 7 shows a second explanatory view of the processing step of the emitter of this embodiment. The above wafer is patterned and developed using an electron beam lithography apparatus (F511 2 + VD 01, ADVANTE TEST) to form an electron beam resist mask 96 having a square frame shape with a period of 0.96 μm and a side of 0.8 μm. did.

  FIG. 8 shows a third explanatory view of the processing step of the emitter of this embodiment. Dry etching (atomic beam etching) using SF 6 gas was performed for a short time to remove the aluminum film exposed in the opening, and an aluminum mask 97 was formed. FIG. 9 shows a fourth explanatory view of the processing step of the emitter of this embodiment. After forming the Al mask, the etching gas is switched to oxygen, and the organic photoresist is selectively etched to obtain a photoresist mask 98 with a high aspect ratio. FIG. 10 shows a fifth explanatory view of the processing step of the emitter of this embodiment. The etching gas is again switched to SF 6, and the Ta and W in the openings are etched by dry etching from above the mask to pattern a square opening with a depth of 1.4 μm, the Ta cap layer 92 ′ and the tungsten light emitting structure Formed 99. FIG. 11 shows a sixth explanatory view of the processing step of the emitter of this embodiment. Again, the etching gas was switched to oxygen to remove the resist remaining on the sample surface. The light emitting structure according to the first embodiment in which the micropore array is formed is manufactured by the above-described steps.

When the micropore distance is 1 μm or less, the electron beam exposure method is used, but when the micropore distance is larger than 1 μm, the ordinary optical exposure method using mercury g-line etc. A light emitting structure can be formed. By annealing the obtained light emitting structure to 800 ° C. or higher in a vacuum, the hydrogen contained therein can be removed, and the life can be increased.
Second Embodiment
[Description of structure]
A light emitting structure according to a second embodiment of the present invention has a single crystal Cr (chromium) body, a Ta cap layer and a Ta2 O5 oxide film. The emitter having the light emitting structure of this embodiment is a plate-like emitter having a length of 25 cm, a width of 5 cm, and a thickness of 5 mm. The TPV device to which the light emitting structure of the present embodiment is applied has an octagonal shaped emitter in which the above plate shaped emitters are combined into an octagonal shape. The micropores of the light emitting structure of this embodiment are periodically formed in a square grid shape on the outer surface of the octagonal prism. The TPV system to which this embodiment is applied is a portable emergency power generation system using methane gas as a fuel, a simple system configuration that does not use a wavelength filter, an output temperature of 1 kW, and a power generation efficiency of 15% at an emitter temperature of 1400K. was gotten.

  FIG. 12 shows the appearance of the surface portion of the light emitting structure according to the second embodiment and the cross section thereof. The light emitting structure 100 of the second embodiment comprises a light emitting structure 101 of single crystal Cr and a Ta cap layer 102 formed on the surface thereof, and micropores 103 are periodically formed on the surface in a square lattice shape. It is done. A Ta 2 O 5 oxide film 108 is formed on the surface of the light emitting structure 101, and a Cr 2 O 3 oxide film 109 is formed on the side wall of the fine hole 103. The thickness t_cap of the cap layer is 0.30 μm. The period Λx104 of the micropores and the period 微細 y105 are both 1.2 μm. The aperture shape of the fine hole 103 is circular, the diameter D106 of the open circle is 0.9 μm, and the depth t107 of the hole is 1.5 μm. The Λ / D ratio (= 1.2 / 0.9) is 1.33, and the t / D ratio (= 1.5 / 0.9) is 1.67. The t_cap / t ratio (= 0.30 / 1.5) is 0.20. The melting point of Ta 2 O 5 is 1468 ° C., which is comparable to the melting point 1473 ° C. of WO 3. The melting point of Cr 2 O 3 is as high as 2435 ° C. The Ta2O5 oxide film 108 and the Cr2O3 oxide film 109 are transparent to infrared light, and therefore do not affect the shape of the radiation spectrum obtained at the time of heating.

  Here, the relationship between the period 微細 of the micropores, the depth t of the micropores, the opening diameter D, and the cap layer thickness s will be described.

  Regarding the period Λ, when the period Λ exceeds 2D (Λ / D exceeds 2), the ratio of the area occupied by the holes decreases and the peak intensity of the emissivity decreases.

  With regard to the depth t of the micropores, the aperture diameter D or more is desirable, and in the case of the light emitting structure 101 using an ordinary metal, sufficient effects can be obtained within 2D to 3D. There is no particular limitation on the depth t at which the effect can be obtained, but it is difficult in terms of processing technology to make a hole having an aspect ratio (t / D) of 20 or more, and it is practical to set the upper limit to about 20.

The peak intensity of the emissivity spectrum is 0.9 or more when the cap layer is made of a material having a high emissivity in the peak wavelength region ( Ta in this embodiment 2) and 1.08 ≦ Λ / D ≦ 2 and 1 ≦ t / D ≦ 20. You can The emissivity spectrum is wavelength dependent of the emissivity, and takes a value of 0-1. The fact that the peak intensity of the emissivity spectrum can be set to 0.9 or more means that the peak intensity can be set to 0.9 or more at an emissivity at which the maximum is 1.

  If the cap layer is made of a material with a high emissivity in the peak wavelength range and the thickness s of the cap layer is set to 1/20 s s / t 1/2 1⁄2 with respect to the depth t of the micropores, the spectral width is narrow Can be For example, when λp = 1.6 μm, the 1 / e wavelength full width δ of the thermal emission spectrum can be narrowed to 0.6 μm at an emitter temperature of 1400 K. Since the total wavelength width of the thermal emission spectrum at 1400 K of the light emitting structure of Cr alone without a cap layer is 3 μm, the spectrum width can be narrowed to 1⁄5 by the Ta cap layer. The photoelectric conversion efficiency of the photoelectric conversion element decreases with distance from the compatible wavelength toward the short wave side, and becomes zero at a wavelength larger than the compatible wavelength.

  With regard to the cap layer thickness s, the effect of high wavelength narrowing is obtained at 0.2 μm or more, but the effect occurs even if s is 0.1 μm (s = t / 20 = 2 μm / 20 = 0.1 μm). With respect to the upper limit of s, it is desirable that the upper limit of s be kept smaller than or equal to half because the emissivity is lowered when s is larger than half of the depth of the micropores. The maximum depth at which light with a wavelength of 2 μm penetrates the metal is about 0.1 μm at the maximum, but the edge of the micropores is likely to penetrate, so the cap layer should be thicker than 0.1 μm. The area where light penetrates may be covered with a cap layer with very low light absorption.

  FIG. 13 shows the appearance of the TPV power generator of the second embodiment, FIG. 14 is a cross-sectional view of the TPV power generator of the second embodiment, and FIG. 15 is a top view of the TPV power generator of the second embodiment. The TPV power generation apparatus of the second embodiment includes a support 110, a methane introduction pipe 111, an air introduction pipe 112, a support leg 113, an air-fuel mixture introduction pipe 114, a radiation fin 115, a PV element 116, an octagonal emitter 117, and a bar. And the flame vent 119, the heat insulating plate 120, the vent 121 and the like. The octagonal emitter 117 is formed by combining an emitter plate on which eight light emitting structures 101 are formed.

  FIG. 16 shows a cross section of the emitter junction of the second embodiment. The light emitting structure 100 is firmly joined by inserting a female chromium plate 123 and a male chromium plate 124 which are formed on the outer side into each other at a joint portion 122. The octagonal emitter 117 is supported by the heat insulating plate 120, the support leg 113 of stainless steel and the support base 101. The heat insulating plate 120 is installed so as not to transfer the heat of the octagonal emitter 117 to the PV element 116. A small air vent 121 is opened in the heat insulating plate 120 and functions to expel the heated air between the octagonal emitter 117 and the PV element 116 to the upper part by using the outside air taken in from the lower part. The PV element 116 is a GaSb-based photoelectric conversion element disposed opposite to the octagonal emitter 117. The radiation fin 115 is made of aluminum.

  The operation method of the TPV power generator of the second embodiment will be described. Methane and air are supplied at a predetermined mixing ratio through the methane introducing pipe 111 and the air introducing pipe 112, are supplied to the burner 118 through the mixture introducing pipe 114, and are burned at the flame port 119. The igniter is installed beside the flame opening. A high temperature flame and exhaust gas heat the octagonal emitter 117 from the inside. An exhaust gas consisting of CO 2 and water vapor is emitted from the top of the octagonal emitter 117 to the outside. The infrared light emitted from the octagonal emitter 117 is received by the surrounding PV element 116 to generate electric power. The heat generated by the electrical resistance of the PV element is radiated from the heat radiation fin 115 on the back side. In order to prevent the heating of the PV element, the radiator fins are air-cooled and operated by a fan from the outside as needed.

[Description of effect]
FIG. 17 shows emissivity spectra of Ta and Cr flat plates. Cr is inexpensive and easy to process, but has a wide emissivity spectrum. The emissivity of the Cr flat plate shows a constant value of emissivity of about 0.45 up to a wavelength of 2.5 μm. On the other hand, Ta is a small value of emissivity 0.05 or less at a wavelength of 1.3 μm or more. By combining these, a narrow heat radiation spectrum is obtained.

  FIG. 18 shows the thermal radiation spectrum (1400 K) of the light emitting structure of the second embodiment. Black-body radiation (BB), Cr-only light emission structure, Ta cap layer 100 nm light emission structure, Ta cap layer 300 nm light emission structure, Ta-only light emission structure The thermal emission spectrum at 1400 K is shown. The diameter D of the micropores of this example was 0.9 μm, and the peak wavelength of the obtained thermal emission spectrum was 1.6 μm (<2 · D). Light having a wavelength of 1.6 μm or less can form a standing wave in the space inside the fine hole. Standing waves with a wavelength of 1.6 μm or less are well absorbed by Cr in the vicinity of the surface of the micropores. This means that light with a wavelength of 1.6 μm or less is emitted to the outside from Cr near the wall surface of the fine pore. On the other hand, light having a wavelength of more than 1.6 μm can not form a standing wave in the micropores, so it is not emitted from the micropores to the outside, but emitted from the surface of the Ta cap layer other than the micropores to the outside. As shown in FIG. 17, since the emissivity of Ta at a wavelength of 1.6 μm or more is lower than that of Cr, the emission of light having a wavelength of more than 1.6 μm is significantly suppressed.

  Therefore, in the light emitting structure of the present embodiment, it is considered that the emission spectrum is narrowed because the light near the wavelength of 1.6 μm is strongly emitted and the radiation of the light having the wavelength larger than 1.6 μm is suppressed.

  While the thermal emission spectrum of the Cr-only light emission structure has a 1 / e width of 3 μm or more, a narrow thermal emission spectrum of 0.7 μm in width was obtained in the 300 nm light emission structure of the Ta cap layer of this example. . By thickening the Ta cap layer from 100 nm to 300 nm, the emission spectrum width can be made smaller without lowering the peak power. This is considered to be because the thermal radiation from Cr could be prevented from being emitted to the outside by setting the thickness of the Ta cap layer to 0.3 μm or more.

  The obtained output was 1.05 kW. Since the element area was 1000 cm 2, the output per unit area was 1.05 W / cm 2. The radiant energy calculated from 32% of the device efficiency was 15% of the energy of black body radiation. The overall efficiency was 15% from the combustion efficiency of 65%, the spectral efficiency of 72%, and the PV element efficiency of 32%. This corresponds to the efficiency of the machine engine. It is expected that a power generation efficiency of 23% can be obtained by improving the spectral efficiency to 85% by adjusting the combustion efficiency to 85% and the peak wavelength.

  Although a single crystal Cr plate is used in the present embodiment, the effect of the present embodiment can be obtained even if a normal polycrystalline Cr plate is processed. The light emitting structure and the TPV power generator of this embodiment can be obtained by using a polycrystalline Cr plate cheaper than tungsten crystal.

  The Cr2O3 oxide film formed by heat sensing in the air is superior in oxidation resistance at high temperature than the WO3 oxide film. Also, because of the Cr2O3 oxide film, the fine structure of the light emitting structure formed on the polycrystalline Cr plate can be maintained even at high temperature. Therefore, a high output and long life emitter can be obtained. A small amount of Ni, Co, or the like may be added to Cr of the light emitting structure main body to make the emitter tenacious to mechanical impact.

In order to apply the tungsten surface diffraction grating of Non-Patent Document 5 shown in FIG. 37 of the background art to TPV power generation etc., it is necessary to use a tungsten single crystal having high oxidation resistance. A large area tungsten single crystal is required to obtain a large output, but it is expensive. Further, since tungsten single crystal is very hard, it is costly to precisely process a wide range of fine holes on its surface in a wide range. Although non-patent document 5 uses expensive and hard metals such as W and Mo, emitters having relatively high melting points such as easy-to-process and inexpensive Cr (chromium), V (vanadium) and Zr (zirconium) can be used as an emitter It is desirable to be able to use it. FIG. 39 shows emissivity spectra of Cr, Zr, V, W flat plates obtained by the present inventors by experiments. Cr and Zr have high emissivity over a wide range of 0.3 μm to 3 μm or more. Particularly in the wavelength band of 1.7 μm or more, the emissivity of Cr, V, and Zr is significantly higher than the emissivity of W. Therefore, when these inexpensive metals are used, the emission spectrum width of both flat plate emitters and diffraction grating emitters becomes wide, which causes a problem that the power generation efficiency of the thermal photovoltage is lowered.

  As a technology related to this problem, the article "Photo Crystal-Enhanced Narrow-Band Infrared Emitter" in Non-Patent Document 6 describes an emitter using silicon which is easily microfabricated. Specifically, this is an infrared emitter in which a gold thin film is deposited on the surface of a silicon semiconductor wafer, and circular fine holes are periodically formed in a square arrangement. Optical radiation in the 4 μm band at 325 ° C. is obtained. The narrowing principle of the wavelength spectrum of the emitter of Non-Patent Document 6 is due to the surface plasmon effect of a gold thin film in which circular fine holes are periodically formed.

On the other hand, the tungsten diffraction grating of Non-Patent Document 5 utilizes the microcavity effect of metal to electromagnetic waves, and the narrowing principle of the wavelength spectra of the two is completely different. W strongly emits visible light and infrared light, but the emissivity of Si is large mainly in the visible light region of 0.8 μm or less, and infrared light of 1.1 μm or more is not emitted at all. In other words, the Si wafer holds the gold thin film and plays only the role of providing fine pores. In fact, if Si is replaced with a metal such as W, the surface plasmon effect of the Au thin film is lost. In addition, thin films with large surface plasmon effects are limited to Au, Ag, and the like. The melting point of Au is 1064 ° C., the melting point of Ag is 962 ° C., and can not withstand the temperature of 1000 ° C. or more used in TPV power generation. Also for silicon, a temperature of about 1000 ° C. is a practical limit. Further, there is a difference in thermal expansion coefficient between the silicon semiconductor and gold, and there is a problem that the gold peels off at high temperature. This limits the life and output. Therefore, the emitter of Non-Patent Document 6 can only be used as a mid-infrared light source for spectroscopy used at a temperature of about 300.degree.

  There is also a method of forming a Ta2O5 oxide film directly with a reactive sputtering apparatus. In order to form an oxide protective film on the surface, a Ta2 O5 layer is formed in advance on the Ta surface by Ta and oxygen plasma by adding O2 at a flow rate of 50 to 200 sccm in an RF or reactive sputtering apparatus. As an etching gas for dry etching of the Ta2O5 layer, a mixed gas of CF4 and O2 (mixture ratio of O2 gas of 10% to 40%) can be used. The etching conditions are, for example, CF 4: 40 sccm, O 2: 10 sccm, pressure: 400 mTorr, and high frequency power: 300 W. The etching rate of tantalum oxide is 0.3 μm / min at a mixing ratio of 20% of O 2 gas.

Ta in the Ta2O5 layer reacts with fluorine to become fluoride, and oxygen in the Ta2O5 layer reacts with carbon to become CO and CO2, and is effectively etched. Since the deposition reaction of the polymer mainly composed of carbon suppresses the etching on the resist surface, the etching rate is lowered, so that the selectivity of tantalum oxide to the resist is improved. As the mixing ratio of O 2 gas was lowered, the selectivity to the resist was improved.
Third Embodiment
[Description of structure]
The third embodiment of the present invention is a triangular grating periodic circular aperture light emitting structure having an oxide protection layer and an intermediate layer, and is used for the emitter of the TPV device of the second embodiment. FIG. 19 shows the light emitting structure of the third embodiment. The light emitting structure according to the third embodiment comprises a light emitting structure 130, a Cr main body 131, a Cr2Ta intermediate layer 132, a Ta cap layer 133, a Cr2O3 protective layer 134, circular fine holes 135, and a triangular lattice period Λ136. The Cr 2 Ta intermediate layer 132 is 100 nm thick, and the Ta cap layer 133 is 0.3 μm thick. The total thickness t_cap of these is 0.40 μm. The Cr 2 O 3 protective layer 134 is 100 nm thick. The Ta cap layer 133 may contain 1 w% to 20 w% of Cr. In order to suppress the increase in the emissivity of the Ta cap layer, the content of Cr is preferably 20 w% or less. Furthermore, 1 w% to 5 w% of B (boron) may be added to obtain a dense thermal oxide film. By adding Cr to Ta, a dense Cr2O3 film is formed on the surface of the Cr: Ta cap layer and the cross section of the opening by heating in the atmosphere. A thermal oxide film such as Cr2O3 is also formed on Cr of the main body of the fine pore surface. The melting point of Cr2O3 is 2435 ° C., the melting point of Cr is 1863 ° C., the melting point of Ta is 3020 ° C., and the melting point of Cr: Ta is 2000 ° C. or more, so it can withstand heating to 1600 ° C.

The triangular lattice period of the micropores is 1.2 μm. The aperture shape of the fine holes 135 is circular, and the diameter D of the circle is 0.9 μm, and the depth t of the holes is 1.6 μm. The Λ / D ratio (= 1.2 / 0.9) is 1.33, and the t / D ratio (= 1.6 / 0.9) is 1.78. The t_cap / t ratio (= 0.40 / 1.6) is 0.25. Assuming that the radius r of the circular opening, in the case of a triangular lattice of period 割 合, the ratio of the area of the opening to the plane surface is given by the following equation 1 .
(2π (D / 2) ² ) / (√3 × Λ ² ) (Equation 1)
In the case of the present embodiment, the ratio of the area of the opening is 51%. In the case of a square grid, the ratio of the area of the opening is given by the following equation 2
π (D / 2) ² / Λ ² (equation 2)
For the same radius and period, the percentage of the area of the opening is 44.2%. In the case of the triangular lattice, the ratio of the area of the opening is about 15% larger than in the case of the square lattice. In the case of a triangular lattice, the same radiation spectrum shape and narrowing effect as in the case of a square lattice are obtained, and the peak emissivity is slightly improved due to the high density of the holes.

  The material of the structure of the present invention will be described. In the first to third examples, W or Cr was used as the metal element A contained in the material of the main body of the light emitting structure. However, as the metal element A used as the main body of the light emitting structure of the present invention, Zr, V, Ti or Mo, Nb, Hf may be used. Alternatively, an alloy that has improved heat resistance, oxidation resistance, workability, flexural strength, etc. by adding Fe, Ni, Co, Cu, Al, Si, etc. to the metallic element A within the range that the melting point does not fall below 1000 ° C. May be used. Alternatively, a small amount of Re, Os, Ir, Pt, Au or the like may be added to the metal element A to improve the processability and the like.

  FIG. 20 shows emissivity spectra of Cr, Zr, V and W flat plates. They have high melting points of 1860 ° C. or higher, and Cr and Zr (zirconium) have high emissivity of 0.3 to 0.4 in a wide range of wavelengths of 0.2 to 3 μm. Alternatively, V (vanadium) has an emissivity 0.2 equal to W at 1.6 μm to 1.7 μm. By using these materials for the main body, strong heat radiation from the surface inside micropores can be obtained by the microcavity effect. An alloy of these refractory metals can also be used as a material. For example, the inclusion of 5 (atomic%) Ta in the Mo cap layer significantly improves the oxidation resistance. The melting point of TaMo is 1820 ° C. or more, and TaMo is thicker than Ta and is resistant to thermal shock due to temperature change.

  In the first to third embodiments, Ta is used as the metal element B contained in the material 2 of the cap layer, but W, Mo, Nb, or Hf may be used as the metal element B. FIG. 21 shows emissivity spectra of W, Mo, Nb, and Ta flat plates. The emissivity of Mo, Nb and Ta is smaller than 0.1 at 1.6 μm or more near the photoelectric conversion wavelength.

  By using a high emissivity metal near the conversion wavelength for the main body of the light emitting structure and a low emissivity metal for the cap layer, a narrowing effect of the emission spectrum can be obtained. These are high melting point metals which allow them to be used at high temperatures and provide strong thermal radiation.

In addition to the metal element B, a material obtained by adding an element C such as Cr, Si, Al, V, Zr, Ca, Mg, or Ag at a concentration of 1 w% to 20 w% as the material of the cap layer is used. Good. When 1 w% or more of these elements C is added, an oxide film is formed on the surface of the cap layer at the time of heating in the atmosphere, as described below. A dense oxide film can be obtained by adding 5 w% to 10 w% of the element C. The addition of the element C lowers the melting point of the cap layer and increases the emissivity of the cap layer, so the concentration of the element C is limited to 20 w%.
[Description of effect]
FIG. 22 shows an Ellingham diagram of the oxide used in the third embodiment. Ellingham diagram (Ellingham diagram) is the figure which displayed the standard formation Gibb's energy of the oxidation reaction in each temperature with respect to various oxide. The standard Gibbs energy of formation is the change amount of Gibbs free energy by the oxidation reaction per 1 mol of oxygen molecule. There is an advantage that materials having different numbers of oxygen contained in the composition formula can be compared with each other.

  From this figure, it is possible to know the reducing agent for reducing the metal oxide to metal and the reduction temperature, or the oxygen partial pressure which can be present without the metal being oxidized. Since the graph is on the upper right, it can be understood that the metal is easily oxidized as the temperature rises. Carbides such as SiC and WC have small temperature dependence. WO3 is more stable than WC. In general, oxides are more stable than carbides. The melting point of the oxide is as high as 2000 ° C. or higher. Therefore, an oxide is suitable for the protective film of metal. However, since WO3 and MoO2 intersect with the H2O and CO2 graphs at 600 ° C. or higher, it is understood that they react with these gases at high temperatures.

  The oxides are listed in a stable order: CaO, MgO, Al2O3 groups are the most stable, then SiO2, V2O3, Ta2O5, NbO2, Ti3O5, Cr2O3 groups, then WO3, MoO2, FeO Finally, the group is IrO3. CaO and MgO are most stable protective films if the film quality is good. In fact, the oxide film of WO3 or MoO2 formed in the materials of W and Mo in Non-Patent Document 5 is oxidized when it is heated to 500 ° C. or higher in the atmosphere, so that the thickness thereof increases. If Ta2O5 or NbO2 is also heated to 300 ° C. or more in the air, oxidation may proceed. Therefore, when used at a very high temperature, a protective film may be necessary for Ta, Nb and Hf. The progress of oxidation also depends on the compactness of the oxide film. Therefore, oxidation resistance is not necessarily determined only by Ellingham diagram. It is SiO2, Cr2O3 and Al2O3 that a dense oxide film is easily obtained. VO2 and ZrO2 also form a strong film. In this embodiment, such an oxidation resistant oxide is formed on the surface of the cap layer of Ta, Nb or Hf to be protected. Alternatively, in this embodiment, a Cr: Ta cap layer containing several percent of Cr in Ta is formed and heated in the air to form a dense Cr2O3 protective film on the surface. The melting point of Cr 2 O 3 is 2435 ° C., for example, Cr 3 O 4 having a melting point of 1660 ° C. has higher oxidation resistance. The Cr2O3 protective film has high oxidation resistance, and thus functions to protect the Ta cap layer from oxidation when heated in the air. Since the Cr2O3 protective film has a large band gap and is transparent, the emissivity of the surface is determined by Ta. Since the Ta cap layer can suppress the emissivity in the wavelength region of 1.3 μm or more, the same radiation spectrum narrowing effect can be obtained also in this embodiment.

The melting point of Cr 2 Ta used in the intermediate layer is 2020 ° C., which is higher than the melting point 1863 ° C. of Cr. Therefore, it has the effect of suppressing the mutual diffusion of Ta atoms and Cr atoms at high temperatures. The Cr2Ta intermediate layer 132 has a melting point of 1760 ° C. when the composition of Cr is higher than that, but maintains a relatively high melting point. The thermal expansion coefficient (1 / K) of Cr depends on temperature and is 7 to 12 × 10 −6 (100 ° C. to 1250 ° C.). The thermal expansion coefficient (1 / K) of Ta is 6.5 to 7.3 × 10 −6 (100 ° C. to 1200 ° C.). Although the thermal expansion coefficients of Cr and Ta are approximately the same, stress occurs at the interface of Cr and Ta at high temperatures. Since the thermal expansion coefficient of Cr is larger than the thermal expansion coefficient of Ta, compressive stress is applied to Ta, but because Ta is strong against compressive stress, the Ta cap layer does not peel off. Since the Cr2Ta intermediate layer has a thermal expansion coefficient intermediate between Cr and Ta, it has an effect of relieving the difference between the thermal expansion coefficients of Ta and Cr and the stress. The Cr2Ta intermediate layer also has the effect of enhancing the adhesion between the Cr main body and the Ta cap layer. For the intermediate layer of this embodiment, an alloy consisting essentially of the material of the main body and the material of the cap layer is used. The effects of these protective layers and interlayers increase the lifetime of the light emitting structure. As a result, by applying the light emitting structure of this embodiment to the emitter, it is possible to provide an inexpensive and long-life TPV power generator.
[Description of manufacturing method]
The light emitting structure of the third embodiment can be manufactured by the same manufacturing method as that of the light emitting structure of the second embodiment, except that the pattern of the openings is changed to the setting of a circular opening with a triangular grating period. Cr2Ta used for the intermediate layer was formed using both a Cr target and a Ta target while controlling the composition by changing the sputtering time and the intensity. To form a Cr2O3 protective film on the Ta surface, O2 is added at a flow rate of 50 to 200 sccm in a reactive sputtering apparatus, and a Cr2O3 layer is formed on the Ta surface with Cr and oxygen plasma. As an etching gas for dry etching of the Cr2O3 layer, a mixed gas of CF4 and O2 (mixture ratio of O2 gas of 10% to 40%) can be used. The etching conditions are, for example, CF 4: 40 sccm, O 2: 10 sccm, pressure: 400 mTorr, and high frequency power: 300 W. The etching rate of chromium oxide is 0.4 μm / min at a mixing ratio of 20% of O 2 gas.

The Cr in the Cr2O3 layer reacts with the fluorine to form fluorides, and the oxygen in the Cr2O3 layer reacts with the carbon to form CO or CO2, which is effectively etched. Since the deposition reaction of the polymer mainly composed of carbon suppresses the etching on the resist surface, the etching rate is lowered, so that the selectivity of chromium oxide to the resist is improved.
Fourth Embodiment
[Description of structure]
FIG. 23 shows a light emitting structure according to a fourth embodiment of the present invention. The light emitting structure of the fourth embodiment is a square grating periodic circular opening light emitting structure having an oxide film protective layer and an intermediate layer, and is used for the emitter of the TPV device of the second embodiment. The major features of the fourth embodiment are that the micropores have a tetragonal lattice period, that a compound of silicon and metal such as MoSi2 is used for the main body of the light emitting structure, and SiO2 is used for the protective film. is there.

  The light emitting structure of the fourth embodiment comprises a light emitting structure 140, a MoSi2 main body 141, a TaMoSi2 intermediate layer 142, a Ta cap layer 143, an SiO2 protective layer 144, circular micro holes 145, and a square lattice period Λ146. The TaMoSi2 intermediate layer 142 has a thickness of 50 nm, the Ta cap layer 143 has a thickness of 0.6 μm, the SiO 2 protective layer 144 has a thickness of 50 nm, and the square lattice period of the micropores is 1.2 μm. The aperture shape of the micropores 145 is circular, the diameter D of the circle is 0.9 μm, and the depth t of the micropores is 2.7 μm. The Λ / D ratio (= 1.2 / 0.9) is 1.33, and the t / D ratio (= 2.7 / 0.9) is 3.0. The t_cap / t ratio (= 0.6 / 2.7) is 0.22. There is also a method of forming a thermal oxide film of SiO 2 on the surface of the Si: Ta cap layer by putting 5 w% of Si in the Ta cap layer. By melting WSi2 (melting point: 2130 ° C., CTE: 7.9 × 10 -6) or adding B, the melting point and mechanical strength of MoSi 2 can be increased. The melting point of SiO 2 is 1700 ° C., and the thermal expansion coefficient (CTE) is 0.55 × 10 −6 (1 / K). MoSi2 is highly resistant to oxidation at high temperatures, and is a material used as a heater material for furnaces and the like. The melting point of MoSi2 is 2290 ° C. Since the melting point lowers to 1400 ° C. when the Si concentration further increases in MoSi 2, the Mo concentration is set to be slightly higher. Mo3Si having a high melting point of 2020 ° C. may be used for the main body.

  In the fourth embodiment, MoSi2 is used for the main body of the light emitting structure, but as the main body of the light emitting structure, a metal silicon compound such as WSi2, TaSi, MoSi2, NbSi2, HfSi2, CrSi2, ZrSi2, VSi2, TiSi2 is used. It can be used. Alternatively, metal borides of TaB2, W2B5, MoB2, NbB2, HfB2, CrB2, ZrB2, VB2, TiB2, or carbides of TaC, WC, MoC, NbC, CrC, ZrC, VC, TiC, or TaN, WN, MoN, Metal nitrides such as NbN, CrN, ZrN, VN, and TiN can be used. The TiN flat plate has a wavelength of 1.6 μm and an emissivity of 0.2 equivalent to that of the W flat plate, so that it can be used for the main body of the light emitting structure of this embodiment. The high melting point boride materials such as TiB2, ZrB2 and HfB2 can be used for the main body of the light emitting structure of this embodiment because they have high conductivity and high infrared emissivity.

As the main body of the light emitting structure, a metal such as in Examples 1 to 3 or a silicon compound of a metal as in this Example 4, a boride, a carbide, a nitride or an oxide is used, and Al2O3, SiO2, Cr2O3, etc. By forming a thermal oxide protective film, the oxidation resistance of the micropores of the main body can be improved.
[Description of effect]
The melting point of MoO 3 is 795 ° C., and the vapor pressure is high. Therefore, when MoSi 2 is heated to 1000 ° C. to 1200 ° C. in the atmosphere, Mo is released in the form of MoO 3 to form a dense SiO 2 film on the surface of MoSi 2. When the temperature is returned to room temperature, compressive stress is applied to the SiO 2 film, but the SiO 2 film withstands the compressive stress. The electrical conductivity of MoSi2 is 4.6.times.10@6 (1 / .OMEGA.m), which is comparable to that of Cr 6.5.times.10@6 (1 / .OMEGA.m). Free electrons that contribute to electrical conduction function to reflect and absorb light. Therefore, MoSi2 has a high melting point and a high emissivity similar to that of Cr, so that it can be applied to the main body of the light emitting structure of this embodiment. The melting point of MoSi 2 is 2030 ° C., and the thermal expansion coefficient is 8.2 × 10 −6 (1 / K). Since this is slightly larger than the thermal expansion coefficient of Ta, compressive stress is applied to Ta. The melting point of Mo 5 Si 3 is 2150 ° C., and the thermal expansion coefficient is 6.7 × 10 −6 (1 / K), which is almost equal to the thermal expansion coefficient of Ta.
The TaMoSi2 intermediate layer suppresses peeling of the Ta cap layer in order to relieve the stress caused by the thermal expansion difference between the MoSi2 main body and the Ta cap layer. Since the depth t of the micropores and the thickness of the Ta cap layer are large, even if the oxidation of the Ta cap layer proceeds gradually, the Ta layer is difficult to disappear, and the life becomes long.
[Description of manufacturing method]
Since MoSi2 is a high melting point material, it is difficult to produce a bulk material by a general melting method. MoSi2 is manufactured using an arc melting method, a reaction sintering method, a vacuum plasma spray method, a diffusion reaction method, a hot press, HIP or the like. The production process is anoxic. When oxygen is mixed, the SiO 2 glass phase segregates at grain boundaries and softens in a high temperature range to deteriorate creep characteristics. The obtained MoSi2 plate was mirror-polished, and the oxide film on the surface was removed with a sulfuric acid type etchant and an HF type etchant. In a magnetron sputtering apparatus with a back pressure of 1 × 10 -6 Torr, a Ta thin film was deposited to a thickness of 0.65 μm by sputtering on a MoSi 2 plate at a substrate temperature of 300 ° C. Further, a 50 nm thick SiO 2 layer was formed by a plasma CVD apparatus, and heating was performed in nitrogen at 1200 ° C. for 1 hour using a diffusion furnace to diffuse Ta, thereby forming a 50 nm thick TaMoSi 2 intermediate layer.

  After that, circular openings with a diameter of 0.9 μm were patterned in a square lattice cycle using a Cr mask, and micro holes with a depth of 2.7 μm were formed in the SiO 2 layer / Ta layer / MoSi 2 plate by dry etching. As an etching gas for dry etching, a mixed gas of CF 4 and O 2 (mixing ratio of O 2 gas: 10% to 40%) was used. The etching conditions are CF 4: 40 sccm, O 2: 10 sccm, pressure: 400 mTorr, and high frequency power: 300 W. The etching rate of the SiO 2 layer is 0.3 μm / min at a mixing ratio of 20% of O 2 gas.

The Si in the SiO 2 layer reacts with fluorine to become fluoride and is released, and the oxygen in the SiO 2 layer reacts with carbon to be etched as CO and CO 2. Mo in MoSi2 becomes MoF and separates, and oxygen becomes CO and CO2 and is etched.
Fifth Embodiment
[Description of structure]
The light emitting structure of the fifth embodiment is a light emitting structure having a square lattice period and a circular opening with an Al2O3 (sapphire) substrate, a Cr / Ti coated layer, a Ta cap layer, and an Al2O3 protective layer, It is used for the emitter of the TPV device of the second embodiment. A major feature of the fifth embodiment is that a non-metal substrate and a metal coating layer are used in combination. FIG. 24 shows a light emitting structure according to a fifth embodiment of the present invention.

The light emitting structure according to the fifth embodiment includes a light emitting structure 150, an Al2O3 substrate 151, a Cr / Ti coated layer 152, a Ta cap layer 153, an Al2O3 protective layer 154, circular micro holes 155, and a square lattice period. It consists of Λ 156. Regarding the Cr / Ti coating layer 152, the thickness of Ti in close contact with the substrate is 50 nm, and the thickness of Cr which is a light emitting layer is 1 μm. The Ta cap layer 153 is 0.5 μm thick, the Al 2 O 3 protective layer 154 is 0.1 μm thick, and the square lattice period of the micropores is 1.2 μm. The aperture shape of the micropores 155 is circular, and the diameter D of the circle is 0.9 μm, and the depth t of the micropores is 2.5 μm. The Λ / D ratio (= 1.2 / 0.9) is 1.33, and the t / D ratio (= 2.5 / 0.9) is 2.78. The t_cap / t ratio (= 0.5 / 2.5) is 0.20. The melting point of Al 2 O 3 is 2070 ° C., the coefficient of thermal expansion (CTE) is 7.1 × 10 −6 (1 / K), and the coefficient of thermal expansion of Ta is 6.5 to 7.3 × 10 −6 (1 / K) or that of Cr The structure withstands high temperatures because it is relatively close to 7.0-12 x 10 -6 (1 / K). The Al 2 O 3 thermal oxide film can also be formed on the surface of the Al: Ta cap layer by including 5 w% of Al in the Ta cap layer. As a base material of a present Example, not only Al2O3 but ceramics, such as SiC, SiO2, CaO, MgO, BN, can be used.
[Description of effect]
Since an Al2O3 substrate is used, an emitter with high oxidation resistance can be obtained. When a transparent Al2O3 substrate is used, the application of a Cr / Ti coating layer emits thermal radiation from Cr. Since the thermal expansion coefficients of Al 2 O 3, Cr and Ta are close, there is no peeling of the metal layer and the life is long. The spectral narrowing effect is obtained as in the previous example.
[Description of manufacturing method]
FIG. 25 is an explanatory view of a processing step of the light emitting structure of the fifth embodiment. A Cr / Ti coated layer 152, a Ta cap layer 153, and an Al2O3 protective layer 154 are formed on the surface of the Al2O3 base material 151 by reactive sputtering. In the same manner as in the first embodiment, a 0.9 μm diameter circular opening of 1.2 μm square lattice period is patterned using a photoresist mask 157 or the like, and a 2.5 μm deep micro hole is formed by dry etching. did. An inductively coupled plasma etching apparatus was used to form micropores in the Al 2 O 3 substrate 151. The wafer was placed on the lower electrode of the reaction chamber, the air in the reaction chamber was exhausted, and the pressure in the reaction chamber was adjusted to 2 × 10 −3 Pa.

  Thereafter, Cl 2 gas, CH 2 Cl 2 gas and Ar gas were supplied to the reaction chamber at flow rates of 50 sccm, 5 sccm and 20 sccm respectively, and the gas pressure in the reaction chamber was set to 0.6 Pa. Instead of CH 2 Cl 2 gas, BCl 3 gas may be used. A plasma of a reaction gas was generated by supplying high frequency power of 200 W to the excitation coil and supplying high frequency power of 1.0 W / cm 2 to the lower electrode.

As a result of etching by this plasma, an etching rate of 20 nm / min was obtained for the Al2O3 substrate. It took 100 minutes to etch to a depth of 2 μm. Further, Ti / Cr is supplied by reactive sputtering to form a Cr / Ti layer 158 on the bottom and side wall of the micropore. The photoresist 154 and the overlying Cr / Ti lift-off layer 159 were then removed by organic cleaning. By this process, the light emitting structure of the fifth example was obtained.
Sixth Embodiment
[Description of structure]
The light emitting structure according to the sixth embodiment is a light emitting structure with a square lattice period and a circular opening with black alumina, a Ti intermediate layer, a Ta cap layer, and an Al2O3 protective layer, and the TPV device according to the second embodiment. Used for the emitter of The feature of the sixth embodiment is that the main body of the light emitting structure uses black alumina having an emissivity of infrared wavelength.

  FIG. 26 shows a light emitting structure according to the sixth embodiment of the present invention. The light emitting structure of the sixth embodiment comprises a light emitting structure 160, a black alumina main body 161, a Ti intermediate layer 162, a Ta cap layer 163, an Al2O3 protective layer 164, circular fine holes 165, and a square lattice period Λ166. The Ti intermediate layer 162 has a thickness of 50 nm, the Ta cap layer 163 has a thickness of 0.5 μm, the Al 2 O 3 protective layer 164 has a thickness of 50 nm, and the square lattice period of fine pores is 1.2 μm. The aperture shape of the fine holes 165 is circular, the diameter D of the circle is 0.9 μm, and the depth t of the fine holes is 1.5 μm. The Λ / D ratio (= 1.2 / 0.9) is 1.33, and the t / D ratio (= 2.0. / 0.9) is 2.22. The t_cap / t ratio (= 0.5 / 2.0) is 0.25.

  Alumina is used in a container for mounting and protecting IC chips and the like, and black alumina has an advantage that the metal wiring is easy to see. The black alumina of the present embodiment contains about 90% of alumina and metal impurities such as Co, Cr, Fe, Mn, Ni and i. Specifically, the black alumina contains a black ceramic pigment which is a spinel solid solution such as Co-Cr-Fe or Co-Mn-Fe.

  As the black alumina of the present embodiment, alumina containing carbon (C: A1203) can also be applied. Black alumina (C: A1203) is used as a carbon-containing refractory. At high temperatures, alumina and carbon react to form solid Al 4 C 3 and gaseous CO. Black alumina can be applied to the emitter of a TPV power generator because CO has a partial pressure of about 0.1 MPa during normal heating and alumina and carbon do not react up to 2000 ° C.

Instead of alumina, an oxide obtained by adding a black pigment to an oxide material containing zircon (ZrSiO4), Al, Ga, Si, Zr, V, Ge, Ca, Mg and the like may be used.
[Description of effect]
Since the black alumina of this example contains a black ceramic pigment which is a spinel solid solution such as Co-Cr-Fe or Co-Mn-Fe, emissivity in the infrared wavelength range is 0.3 to 0.4. Have. Since there is a Ta cap layer, the same wavelength narrowing effect as in the previous embodiments can be obtained.

The black alumina of this example is resistant to oxidation at high temperatures and can be used by heating to 1400 ° C. in the atmosphere. The thermal expansion coefficient of black alumina is 6.8 × 10 −6 (1 / K), which is approximately equal to the thermal expansion coefficient of the Ta cap layer. Therefore, since the emitter can be heated to a high temperature of 1300 ° C., the output can be improved and the lifetime of the emitter can be increased.
[Description of manufacturing method]
In the manufacturing method of this embodiment, a Ti intermediate layer, a Ta cap layer, and an alumina protective film are formed in a black alumina plate shape by a reactive sputtering apparatus as in the above-mentioned embodiment, and after patterning, inductively coupled plasma etching is performed. The apparatus is used to form micropores in the metal layer and the alumina.
Seventh Embodiment
[Description of structure]
The light emitting structure according to the seventh embodiment is a light emitting structure having a square lattice period and a circular opening with an Er3Al5O12 main body, a Ti intermediate layer, a Ta cap layer, and an Al2O3 protective layer, and the TPV device according to the second embodiment. Used for the emitter of A feature of the seventh embodiment is that a spinel oxide Er3Al5O12 containing rare earth Er is used for the main body of the light emitting structure.

  FIG. 27 shows a light emitting structure according to a seventh embodiment of the present invention. The light emitting structure according to the seventh embodiment comprises a light emitting structure 170, an Er3Al5O12 main body 171, a Ti intermediate layer 172, a Ta cap layer 173, an Al2O3 protective layer 174, circular fine holes 175, and a square lattice period Λ176. The Ti intermediate layer 172 has a thickness of 50 nm, the Ta cap layer 173 has a thickness of 0.5 μm, the Al 2 O 3 protective layer 174 has a thickness of 50 nm, and the square lattice period of fine pores is 1.2 μm. The aperture shape of the fine holes 175 is circular, the diameter D of the circle is 0.9 μm, and the depth t of the fine holes is 1.5 μm. The Λ / D ratio (= 1.2 / 0.9) is 1.33, and the t / D ratio (= 2.0. / 0.9) is 2.22. The t_cap / t ratio (= 0.5 / 2.0) is 0.25.

Although Er3Al5O12 is used as a spinel oxide containing rare earth Er in this embodiment, Er3Ga5O12 or Er3 ( Al, Ga ) 5O12 may be used. When using a Si PV cell with a conversion wavelength of 1 μm as the discharge conversion element of the TPV device, Yb can be used as a rare earth having a radiation band in the 1 μm wavelength band. Examples of the oxide containing Yb include Yb3Al5O12, Yb3Ga5O12, Yb3 ( Al, Ga ) 5O12, and the like. By changing the diameter of the opening of the light emitting structure to 0.65 μm and the depth of the fine holes to about 1.3 μm, thermal radiation in the 1 μm wavelength band can be obtained, and thermal radiation of 1.1 μm or more can be suppressed. .

For the oxide, an oxide material containing Al, Ga, Si, Ge, Ca, Mg, and the like including a rare earth such as Yb and Er can be applied. The oxide is not limited to spinel because the emission from Er and Yb does not depend on the structure of the oxide.
[Description of effect]
When the Er3Al5O12 plate is heated, narrow thermal radiation of 1.5 to 1.6 μm band is obtained due to the electron transition of the f orbital of the Er 2+ ion.

  However, the Er3Al5O12 plate has a tail in the emission spectrum at wavelengths longer than 1.6 μm. This is considered to be due to metal impurities contained in Er3Al5O12 and sintering aids such as SiO2, MgO and Y2O3. In this embodiment, since the Ta cap layer is formed on the Er3Al5O12 plate to form the light emitting structure, it is possible to suppress thermal radiation of wavelengths longer than 1.6 [mu] m. By setting the aperture of the light emitting structure to 0.9 μm, thermal radiation of wavelength 1.5 to 1.6 μm band from Er from the Er 3 Al 5 O 12 plate is enabled. As a result, the narrowing effect of the thermal radiation spectrum of the emitter can be obtained as in the previous embodiments.

Er 3 Al 5 O 12 used in this example has a melting point of 2100 ° C., is resistant to oxidation at high temperatures, and can be used by heating to 1400 ° C. in the air. The thermal expansion coefficient of black alumina is 7.4 × 10 −6 (1 / K), which is close to the thermal expansion coefficient of the Ta cap layer. Therefore, since the emitter can be heated to a high temperature of 1300 ° C., the output can be improved and the life can be extended.
[Description of manufacturing method]
The spinel oxide Er3Al5O12 plate is obtained by crushing powders of Er2O3 and Al2O3 to a particle diameter of several micrometers, combining them, pressing and molding, and sintering in a heating furnace at a temperature of 1600 ° C. for 3 hours in the air. . If necessary, use a small amount of a sintering aid.

In the manufacturing method of this embodiment, a Ti intermediate layer, a Ta cap layer, and an alumina protective film are formed on a spinel oxide Er3Al5O12 plate whose surface has been polished by a reactive sputtering apparatus as in the above embodiment. After patterning, micropores are formed in the metal layer and the alumina by using an inductively coupled plasma etching apparatus.
Eighth Embodiment
[Description of structure]
The light emitting structure according to the eighth embodiment is a light emitting structure of a mid-infrared wavelength band of 2 μm to 10 μm and is used as a light source of a gas detection device for detecting a gas having an absorption wavelength in mid-infrared. . FIG. 28 shows the light emitting structure of the eighth embodiment of the present invention.

  The light emitting structure of this embodiment comprises a light emitting structure 180, a Cr main body 181, a CrNb intermediate layer 182, a Si: Nb cap layer 183, an SiO2 protective layer 184, circular fine holes 185, and a square lattice period Λ186. The CrNb intermediate layer 182 is 50 nm thick, the Si: Nb cap layer 183 is 0.7 μm thick, the SiO 2 protective layer 184 is 20 nm thick, and the micropores have a square lattice period of 2.8 μm. The aperture shape of the micropores 185 is circular, the diameter D of the circle is 2.6 μm, and the depth t of the micropores is 3.0 μm. The Λ / D ratio (= 2.8 / 2.6) is 1.08, and the t / D ratio (= 3.0 / 2.6) is 1.15. The t_cap / t ratio (= 0.7 / 3.0) is 0.23. By putting 5 w% of Si in the Nb cap layer, a dense thermal oxide film of SiO 2 was formed on the surface of the Si: Ta cap layer. The melting point of Nb is 2469 ° C., and the melting point of Cr is 1860 ° C. Although the melting point of the CrNb intermediate layer 162 is slightly low at 1650 ° C. to 1770 ° C., since the light emitting structure of this embodiment is used at a relatively low temperature of about 300 ° C. to 700 ° C., the CrNb intermediate layer can be used. NbW is suitable for the intermediate layer when used at higher temperatures.

  FIG. 29 shows a cross-sectional view of the infrared gas detector of the eighth embodiment. The infrared gas detector of this embodiment includes an infrared light source unit 190, a rotary chopper 198, a measurement cell unit 196, and a detector unit 197.

  The infrared light source unit 190 is provided on the opposite side of the heating chopper 192 and the electric wire 191 for supplying electric power thereto, the light emitting structure 193 provided on the heater, and the rotating chopper 198 with the light emitting structure 193 interposed therebetween. A mirror 194 and a wavelength selection filter 195 provided between the light emitting structure 193 and the measurement cell unit 196 are provided. The rotary chopper 198 is located between the infrared light source unit 190 and the measurement cell unit 196 and is rotated by the synchronous motor 199. The measurement cell unit 196 includes a detection gas introduction unit 203, an optical path 205, and a detection gas discharge unit 204. The detector unit 197 has a front chamber 200 and a rear chamber 201, and has a heat flow sensor 202.

  When the inside of the infrared light source unit 190 is decompressed, the life of the wavelength selection filter 195 is increased. The detection gas is introduced from the detection gas introduction unit 203 of the measurement cell unit 196 and discharged from the detection gas discharge unit 204. The detector heats the infrared light source unit 190 to generate infrared light of a desired wavelength by the wavelength selection filter 195, and heats the intensity of the infrared light absorbed and attenuated by the measurement gas of the measurement cell unit 196. It is an apparatus which calculates | requires from the resistance change of the flow sensor 202, and calculates measurement gas concentration. The measurement principle of the apparatus of this embodiment is non-dispersive infrared absorption (NDIR), which is used as a gas concentration analyzer for a process.

The operating principle of the device will be specifically described below. The infrared light emitted from the light emitting structure 193 electrically heated by the heater portion 192 is selected by the wavelength selection filter 195 and detected by the wavelength selection filter 195, and is interrupted at a constant cycle by the rotary chopper 198. Thereafter, the light passes through the optical path 205 in the measurement cell portion 196, is partially absorbed by the measurement gas flowing into the measurement cell, and reaches the detector portion 197. The detector 197 includes a front chamber 200 and a rear chamber 201, in which the same gas as the measurement component gas is enclosed. Both chambers are connected by a thin passage, and a heat flow sensor 202 is installed between them. The infrared rays reaching the detector are first absorbed in part in the antechamber, and then absorbed in the rear chamber. The volume of the enclosed gas in the front and rear chambers expands in proportion to the amount of absorption, so a pressure increase occurs in both chambers. The flow of minute gas generated in the passage connecting the two chambers by the pressure difference is detected by the resistance change of the heat flow sensor 202, and the measurement gas concentration is calculated by the Lambert-Beer equation in which the light absorption coefficient of the medium is known from the attenuation amount of light. Do.
[Description of effect]
The thermal radiation spectrum (600 K) of the light-emitting structure of the eighth embodiment of the present invention is shown in FIG. Blackbody radiation is a calculated value at 600K. The radiation intensity of the light emitting structure was corrected by the emissivity of SiC. The thermal emission spectrum of the light emitting structure of the same diameter aperture of Cr only without the Nb cap layer has a peak wavelength of 5 μm and a broad spectrum width. The thermal radiation spectrum of this example was a spectrum with a half width of 4 μm having a strong peak around a wavelength of 4.3 μm.

  Molecules composed of hetero atoms have the property of absorbing infrared rays of specific wavelengths in the infrared region (2 to 15 μm wavelength band). Carbon monoxide (CO) has a wavelength of the strongest absorption near 4.7 μm and carbon dioxide (CO 2) near 4.3 μm. This device uses a wavelength selection filter to select the absorption wavelength of 4 μm band gas.

  Due to the wavelength narrowing effect of the present embodiment, wavelength light effective for detection is efficiently generated, and the infrared gas detector of the present embodiment has the effect of being able to detect the concentration of several ppm of CO 2 or CO gas with high sensitivity. According to this embodiment, an inexpensive mid-infrared light source can be provided without using a mid-infrared expensive laser element. The heat radiation structure of this embodiment emits light in the 3 to 4 μm band, which has a high snow melting effect, and thus can be used as a light source for a snow melting apparatus. Nb in the cap layer is a metal with a large amount of production among high melting point metals, and there is an advantage that mass production can lower the cost.

  The mid-infrared region with a wavelength of 3 μm to 10 μm is referred to as a fingerprint wavelength region, and is a wavelength region where a gas or a molecule can be identified by absorption of a functional group. However, there is no inexpensive light source in the mid-infrared region. In fact, most of the emission wavelengths of the semiconductor laser and the LED light emitting element are 2.5 μm or less, the emission wavelength of the Er-YAG solid laser is 2.9 μm, and the wavelength of the carbon dioxide gas laser is 10.6 μm.

Quantum cascade laser devices have an oscillation wavelength in the mid-infrared region, but are expensive light sources. In addition, since the spectrum width is very narrow, it is difficult to adjust the oscillation wavelength to the absorption wavelength of gas molecules. When the non-linear optical effect of a crystal is used, there is a problem that the apparatus becomes large and the efficiency is significantly reduced. In addition, a tungsten diffraction grating emitter can not be used as a mid-infrared light source because its radiation spectrum with a wavelength of 3 μm or more is small. Even when other metals are used as the emitter, there is a problem that only the mid-infrared region can not be efficiently emitted for gas detection or molecular identification. However, according to this embodiment, the light source in the mid-infrared region can be provided inexpensively.
[Description of manufacturing method]
The light emitting structure of the eighth embodiment can be manufactured in the same manner as the light emitting structure of the third embodiment.
[The ninth embodiment]
[Description of structure]
The light emitting structure of the ninth embodiment is a light emitting structure of visible light wavelength band of wavelength 0.4 μm to 0.7 μm and is used for a filament for illumination. FIG. 31 shows the light emitting structure of the ninth embodiment of the present invention. The light emitting structure of the ninth embodiment comprises a light emitting structure 210, a W crystal main body 211, an AgW cap layer 212, circular fine holes 213, and a square lattice period Λ 214. Ag of the AgW cap layer 212 has a concentration of 20 atomic% to 30 atomic%, and the layer thickness is 0.2 μm. The period Λ of the circular fines 213 is 0.36 μm, the opening shape is circular, the diameter D of the circle is 0.24 μm, and the depth t of the fine holes is 0.6 μm. The Λ / D ratio (= 0.36 / 0.24) is 1.5, and the t / D ratio (= 0.6 / 0.24) is 2.5. The t_cap / t ratio (= 0.2 / 0.6) is 0.33. Instead of AgW, it is also possible to use AgTa having a smaller emissivity in the near infrared as the material of the cap layer 212.

  FIG. 32 shows a cross sectional view of the incandescent lamp of the ninth embodiment. The incandescent lamp of the ninth embodiment comprises a center electrode 220, an external lead wire 221, a base 222, a mount 223, a bulb 224, an internal lead wire 225, a light emitting structure filament 226, an inert gas 227 and an insulating material 228. .

The size of the light emitting structure filament 226 is 10 mm long, 4 mm wide, and 1.5 mm deep. The light emitting structure 210 of the ninth embodiment is formed on the surface of the light emitting structure filament 226. Since the inert gas 227 such as Ar, Kr or Xe is enclosed inside the bulb 224, the light emitting structure is not oxidized even when the filament is heated to about 2500 ° C. by energization. The inert gas may not be sealed in the valve 224 and vacuum may be applied.
[Description of effect]
The emissivity at a wavelength of 0.7 μm is 0.5 for the W plate, 0.2 for the AgW plate, and 0.1 or less for the AgTa plate. By using AgW or AgTa for the cap layer, the emissivity of infrared light having a wavelength of 0.7 μm or more can be suppressed to 0.3 or less. Since W has a high emissivity of 0.5 or more in the visible region, strong visible light radiation can be obtained from the minute apertures formed in the light emitting structure filament upon heating. By adding Ag, the reflectance in the visible region can be further increased, and a filament of a white light bulb can be obtained.

  FIG. 33 shows the thermal emission spectrum (2500 ° C.) of the light emitting structure of the ninth example. The peak wavelength was 0.6 μm and the emissivity at that wavelength was 0.95. The radiant energy of visible light with a wavelength of 0.4 to 0.75 μm of the light bulb of this example was 72% of the total. It was possible to effectively suppress the radiation of wavelength light of 1 μm or more, which was difficult until now. The incandescent lamp of this example provided a lamp efficiency of 105 lumens / W. This efficiency corresponds to 7 times 15 lumens / W of incandescent light bulbs, a value similar to that of fluorescent lights and LED light bulbs. Unlike the fluorescent lamp and the LED bulb, the incandescent lamp of the present embodiment is a natural light suitable for illumination since the wavelength component is continuous. Because the red component is strong, it is more suitable for lighting for home use and food service than for office use.

Patent Document 4 "Incandescent Light Bulbs and Filaments" describes an incandescent light bulb that uses tungsten having a large number of fine holes formed on its surface as a filament. This filament is heated by the electrical resistance at the time of energization. The vacuum sealing prevents oxidation of the filament. As a result, radiation of infrared light with a wavelength of 1.4 μm or more can be suppressed, and the efficiency of the incandescent lamp is said to be improved. In order to further improve the efficiency of illumination, it is desirable to be able to suppress the emission of infrared light having a wavelength of 0.7 μm or more. However, as can be seen from FIG. 39, there is a problem that the radiation of infrared light with a wavelength of 0.7 to 1.4 μm can not be suppressed with tungsten alone. In the present embodiment, as described above, the emissivity of infrared light having a wavelength of 0.7 μm or more can be suppressed.
[Description of manufacturing method]
AgW is formed on both sides of the W crystal substrate by sputtering. In the same manner as above, patterning is performed with an opening diameter of 0.24 μm, and a light emitting structure is formed on the surface by dry etching. The light emitting structure is formed on the front surface by the same process as the back surface. The light emitting structure wafer is cut into the above-mentioned size used for the filament and cut to open a connecting hole inside, and connected to the internal introduction terminal to form the filament. The resulting filament is placed in an incandescent lamp and sealed with an inert gas to produce the incandescent lamp of this example.

The basic structure and materials of the above embodiments are organized. FIG. 34 shows the materials, structures and uses of non-patent document 5 and nine examples of the light emitting structure of the present invention. With respect to the materials, the materials of the main body of the light emitting structure, the intermediate layer, the cap layer and the protective film have been described. Regarding the structure, the periodic structure and the period of the light emitting structure are described. The spectrum describes the peak wavelength of the emission spectrum when the light emitting structure is heated to a temperature of 1100 ° C. The main applications are TPV devices, gas detectors and incandescent bulbs.
[Other embodiments]
FIG. 35 shows the material and structure of another embodiment of the light emitting structure of the present invention. These light emitting structures are an example of a combination of materials of the main body, the intermediate layer, the cap layer, and the protective film of the light emitting structure having a 1.6 μm band emission spectrum for TPV device application. In order to prevent peeling of the cap layer by adjusting the thermal expansion coefficient, the intermediate layer often consists of the material of the body and the cap layer. In the examples, the combination of the main body and the cap layer was selected so that the melting point of the intermediate layer was not lower than that of the main body. Since the light emitting structure of this embodiment is covered with a stable oxide film, many withstand high temperatures of 1100 ° C. or more in the atmosphere. Since the oxide film is transparent in the infrared, it does not interfere with the narrowing effect of the radiation spectrum of this embodiment. Alternatively, when the main body is a high melting point metal, the ductility and the strength may be increased by adding a small amount of Re, Os, Ir, Pt, Au or the like to the high melting point metal. The light emitting structure of these embodiments can provide an inexpensive material and a long-lived emitter for TPV power generation. Also, by changing the structure of the same material, radiation of other wavelength bands can be obtained. Other embodiments will be described below.

  Example 10 is a light emitting structure having micropores of circular openings arranged in a triangular lattice having a Ni: Cr main body, a Cr2Ta intermediate layer, a Si: Ta cap layer, and a SiO2 protective layer. Ni: Cr main body is Cr (Ni (nickel) added with 5 (at%)) to increase the toughness of the main body. In addition to Ni, an element such as Fe, Co, or Cu may be added. The Cr2Ta intermediate layer has a function to suppress peeling between the main body and the cap layer. The Si: Ta cap layer contains Si of 6 (atomic%) in Ta, thereby forming a thermal oxide film of SiO2. A thermal oxide film of Cr2O3 is formed on the Ni: Cr main body.

Example 11 is a light emitting structure having micropores of a circular opening arranged in a square lattice shape having a Ni: Cr main body, a CrW intermediate layer, an Al: W cap layer, and an Al2O3 protective layer. The melting point of CrW, which is the material of the intermediate layer, is 2640 ° C., which is intermediate between the melting point 1860 ° C. of Cr and the melting point 3420 ° C. of W. Since the melting point of CrW increases almost linearly with the increase of the Cr composition, it is an easy-to-use intermediate layer.
Al: W cap layer contains 5% Al in W. Since the melting point of AlW drops sharply to 1650 ° C. when it contains 12% or more of Al, the Al concentration is controlled to within 10%.

  Example 12 is a light emitting structure having micropores of a circular opening arranged in a triangular lattice shape having a Cr main body, a CrMo intermediate layer, a Si: Mo cap layer, and a SiO 2 protective layer. Since Mo (melting point 1623 ° C.), which is a high melting point metal, has an emissivity smaller than 0.1 at a wavelength of 1.6 μm or more, the use of Mo for the cap layer of the light emitting structure of this example results in a narrowing effect of the emission spectrum. can get. The melting point of CrMo used in the intermediate layer is 2000 ° C., which is higher than the melting point 1863 ° C. of Cr. The CrMo intermediate layer has the effect of suppressing the interdiffusion of Cr and Mo at high temperatures. The material of the intermediate layer, CrMo, has a melting point lowered by 40 ° C. at a Cr concentration of 10 (atomic%), but as the Cr concentration is further increased, the melting point of CrMo increases. The thermal expansion coefficient of Mo is 5.2 to 6.0 × 10 −6 (1 / K) (100 ° C. to 1200 ° C.), which is about half the thermal expansion coefficient of Cr. Although a stress is generated at the interface of Cr and Mo at high temperature, the CrMo intermediate layer has an effect of alleviating the stress of Cr and Mo to prevent the peeling of the Si: Mo cap layer.

  Example 13 is a light emitting structure having micropores of a circular opening arranged in a square lattice shape having a Cr main body, a CrNb intermediate layer, a Cr: Nb cap layer, and a Cr2O3 protective layer. The emissivity spectrum of the Nb flat plate is next to Ta. The emissivity of Nb, which is a refractory metal, becomes 1.3 or less at a wavelength of 1.3 μm or more, the use of Nb in the cap layer of the light emitting structure of this embodiment provides a narrowing effect of the radiation spectrum. The thermal expansion coefficient of Nb is 7.0 to 9.2 × 10 −6 (1 / K) (100 ° C. to 1200 ° C.), and the thermal expansion coefficient of Cr is 7.0 to 12 × 10 −6 (1 / K) (100 ° C. to Close to 1200 ° C). Therefore, since the stress applied between the Nb cap layer and the Cr main body at a high temperature is relatively small, the Nb cap layer is hardly peeled off. Nb is a refractory metal whose cost can be reduced by mass production because Nb is higher in ground presence ratio by one digit than other refractory metals. The melting point of CrNb is 1620 ° C., which is lower than that of Cr (1863 ° C.), so the use temperature is limited to 1500 ° C. or less. When W is used in the intermediate layer, melting point depression does not occur due to mutual diffusion between W and Nb, or W and Cr.

  Example 14 is a light emitting structure having micropores of circular openings arranged in a triangular lattice having a Cr: V body, a TaV intermediate layer, a V: Ta cap layer, and a V2O3 protective layer. Cr: V body is V (vanadium) plus 6 w% of Cr. The melting point of V is as high as 1916 ° C. V has an emissivity equivalent to W at 1.6 μm to 1.7 μm. The V body and the Ta cap layer provide a narrowing effect on the emission spectrum. V is cheaper than W and easier to process. The TaV intermediate layer is stable because Ta and V do not cause melting point depression due to mutual diffusion. The thermal expansion coefficient of Ta is 6.5 to 7.3 × 10 −6 (1 / K) (100 ° C. to 1200 ° C.), and the thermal expansion coefficient of V is 8.4 to 9.2 × 10 −6 (1 / K) (100 ° C. to Slightly less than 1200 ° C). Weak tensile stress is applied to the Ta cap layer at high temperature. Since the TaV intermediate layer has an intermediate thermal expansion coefficient, it has the effect of relieving stress and enhancing the adhesion of Ta. V: Ta cap layer is Ta plus 5% V, and forms a V2O3 layer when heated. The V2O3 protective layer is characterized by being a stable and tenacious oxide film. Since the emissivity of V is smaller than that of Cr, the depth of the micropores formed in the V body is made larger than that of the Cr body.

  Example 15 is a light emitting structure having micropores of a circular opening arranged in a square lattice shape having a V body, a VNb intermediate layer, a Cr: Nb cap layer, and a Cr2O3 protective layer. Since the thermal expansion coefficient of Nb 7.0 to 9.2 × 10 -6 is approximately the same as the thermal expansion coefficient of V 8.4 to 9.2 × 10 -6, there is an advantage that the Cr: Nb cap layer is difficult to peel off. The melting point of VN concentration 30 w% of VNb is 1860 ° C., which is smaller than V (melting point 1910 ° C.). The melting point of VN 50 wt% or more of VNb is greater than the melting point of V. Cr: Nb cap layer is Nb plus 5 w% Cr. When heated, a Cr2O3 protective layer is formed on the surface of the Cr: Nb cap layer.

  Example 16 is a light emitting structure having micropores of a circular opening arranged in a triangular lattice having a V body, a VMo intermediate layer, an Mo cap layer, and an MgO protective layer. The melting point of the VMo interlayer is 2100 ° C. The melting point of VMo increases almost in proportion to the Mo concentration. The thermal expansion coefficient of Mo of 5.2 to 6.0 × 10 -6 is smaller than the thermal expansion coefficient of V of 8.4 to 9.2 × 10 -6. Therefore, when the VMo intermediate layer is formed to be slightly thick, the Mo cap layer is not easily peeled off. MgO has a high melting point of 2850 ° C., and if it can be formed densely, it becomes an excellent protective film with high oxidation resistance.

  Example 17 is a light emitting structure having circular apertures micropores arranged in a square lattice shape having a Cr: Zr main body, a TaZr intermediate layer, a Cr: Ta cap layer, and a Cr2O3 protective layer. Example 17 is the structure protected by Cr2O3 using a Zr main body and a Ta cap layer. The Cr: Zr main body is obtained by adding 4 w% of Cr to Zr, and forms a Cr2 O3 thermal oxide film upon heating. The thermal expansion coefficient of Zr is 5.7 to 7.times.10@-6, which is approximately equal to the thermal expansion coefficient of Ta of 6.5 to 7.3.times.10@-6. The melting point of Zr is 1855 ° C., and the melting point of Ta is 3020 ° C. However, when 10% of Zr is contained, the melting point of TaZr falls to 2000 ° C. The melting point of TaZr having a Zr concentration of 10 w% or more is equal to the melting point of Zr. When used at high temperature, the Zr concentration of the TaZr intermediate layer is set to about 5 w% to maintain adhesion. Cr: Ta The cap layer is Ta containing 5 w% of Cr.

  Example 18 is a light emitting structure having micropores of a circular opening arranged in a triangular lattice shape having a Zr main body, a TaZr intermediate layer, a Zr: Ta cap layer, and a ZrO2 protective layer. Example 18 is a configuration in which a Zr body and a Ta cap layer are used and protected by a dense film of ZrO2. There is an advantage that it can be formed only by Zr and Ta.

  Example 19 is a light emitting structure having micropores of a circular opening arranged in a square lattice shape having a Zr body, a ZrNb intermediate layer, a Ca: Nb cap layer, and a CaO protective layer. Example 18 used a CaO protective layer, using a Zr main body and an Nb cap layer.

  The thermal expansion coefficient of Zr is 5.7 to 7 × 10 -6, and the thermal expansion coefficient of Nb is smaller than 7.0 to 9.2 × 10 -6. Since a compressive strain is applied to the Nb cap layer, the cap layer can not be peeled even at high temperature by adding the ZrNb intermediate layer. ZrNb decreases to 1740 ° C. at an Nb concentration of 20 w%, but since ZrNb having a Nb concentration of 50 w% has a melting point equivalent to that of Zr (1655 ° C.), mutual diffusion can be suppressed. CaO has a high melting point of 2570 ° C., and if it can be densely formed, it becomes an excellent protective film having high oxidation resistance.

  Example 20 is a light emitting structure having micropores of a circular opening arranged in a triangular lattice having an Hf body, a ZrHf intermediate layer, an Mg: Zr cap layer, and an MgO protective layer. Although Hf is a relatively expensive metal, it has a high melting point of 2230 ° C. and a large thermal emissivity, so it can be used for the main body of the light emitting structure of this embodiment. There is no melting point depression in ZrHf, and the melting point rises linearly with the Zr concentration. The Mg: Zr cap layer is Zr to which 5% of Mg is added, and forms a MgO protective layer upon heating. The Hf body forms a corrosion resistant Hf2O5 oxide film when heated. In addition to Zr, Ta and W can be used for the cap layer, and there is no melting point drop in the intermediate layer of TaHf and WHf.

  Example 21 is a light emitting structure having micropores of a circular opening arranged in a square lattice shape having a MoSi2 main body, a Mo3Si intermediate layer, a MoTa cap layer, and a SiO2 protective layer. The electrical conductivity of MoSi 2 is 4.6 × 10 6 (1 / Ωm), close to V. MoSi2 can be used in light emitting structures because it has thermal radiation at infrared wavelengths. The melting point of MoSi 2 is 2293 ° C., and the thermal expansion coefficient is 8.2 × 10 −6. The thermal expansion coefficient of MoTa is 6.0 to 6.7 × 10 −6 (100 ° C. to 1200 ° C.), which is slightly smaller than MoSi 2. Tensile strain occurs in MoTa. The stress can be relaxed by inserting the Mo3Si intermediate layer. Use at 1200 ° C or less to prevent peeling of Mo. Since the melting point of the Mo3Si intermediate layer is as high as 2020 ° C., the diffusion of Si into the MoTa cap layer is suppressed.

  Example 22 is a light emitting structure having micropores of a circular opening arranged in a triangular lattice shape having a ZrSi2 main body, a MoZrSi2 intermediate layer, a Si: Mo cap layer, and a SiO2 protective layer. The electrical conductivity of ZrSi 2 is 1.3 × 10 6 (1 / Ωm). ZrSi2 can also be used in light emitting structures as it has thermal radiation at infrared wavelengths. The melting point of ZrSi2 is 1793 ° C. Since ZrSi2 forms a SiO2 thermal oxide film on the surface at high temperature, its oxidation resistance is high. The Si: Mo cap layer is formed by adding 5 w% of Si to Mo, and forms a thermally oxidized SiO2 film on the surface at a high temperature.

  Example 23 is a light emitting structure having micropores of a circular opening arranged in a square lattice shape having a main body WSi2 body, a MoWSi2 intermediate layer, a Si: Mo cap layer, and a SiO2 protective layer. The melting point of WSi2 is 2430.degree. The electrical conductivity of WSi2 is as high as 80 × 10 6 (1 / Ωm), and the thermal emissivity at infrared wavelengths is high, so it is a material suitable for the main body of the light emitting structure. The hardness of WSi2 is about 1/3 of WC, so it is easy to process. Since WSi2 also forms a SiO2 thermal oxide film on the surface at high temperature, the oxidation resistance is high.

  Example 24 is a light emitting structure having micropores of a circular opening arranged in a triangular lattice shape having a TiB2 main body, a Cr2Ta intermediate layer, a Ta cap layer, and a SiO2 protective layer. The electrical conductivity of TiB2 is as high as 11.1.times.10@6 (1 / .OMEGA.m), and the thermal emissivity at infrared wavelengths is high, so it is a material suitable for the main body of the light emitting structure. TiB2 (titanium diboride) is as hard and light as TiC. The melting point of TiB 2 is 3060 ° C., which is similar to that of Ta (melting point 3020 ° C.). TiB2 has high oxidation resistance because a dense thermal oxide film of TiO2 is formed on the surface when it is heated. Since TiB2 is a harder material than TiC, its adhesion to Ta is high. The film formation of TiB 2 can be performed by a magnetron sputtering method using a TiB 2 target. The target of TiB2 is manufactured by bonding sintered TiB2 to a molybdenum or copper back plate with indium. This makes TiB2 less likely to be damaged.

  Example 25 is a light emitting structure having micropores of circular openings arranged in a square lattice shape having a CrB2 main body, a Cr2Ta intermediate layer, a Cr: Ta cap layer, and a Cr2O3 protective layer. The melting point of Cr 2 O 3 is 2435 ° C. The melting point of CrB2 is 2470 ° C., which is higher than the melting point 1863 ° C. of Cr. The electrical conductivity of CrB2 is as high as 3.3.times.10@6 (1 / .OMEGA.m), and the thermal emissivity at infrared wavelengths is high, making it a material suitable for the main body of the light emitting structure. However, since CrB2 is harder than TaC, processing costs for cutting are high.

  Example 26 is a light emitting structure having micropores of circular openings arranged in a triangular lattice having a ZrB2 main body, a Cr2Ta intermediate layer, a Cr: Ta cap layer, and a Cr2O3 protective layer. The electrical conductivity of ZrB 2 is as high as 10.3 × 10 6 (1 / Ωm), and the thermal emissivity at infrared wavelengths is high, so it is a material suitable for the main body of the light emitting structure. The melting point of ZrB 2 is 3470 ° C. and has a melting point comparable to that of W. Cr: Ta cap layer contains 5 w% of Cr and forms a Cr2O3 protective layer upon heating. When the ZrB2 body is heated, a ZrO2 thermal oxide film is formed. As a light emitting structure having a high melting point and high oxidation resistance, a high power emitter can be obtained. As borides for light emitting structures, TaB2, VB2, etc. can be used.

  Example 27 is a light emitting structure having micropores of a circular opening arranged in a square lattice shape having a CrN / Cr main body, a Cr2Ta intermediate layer, a Si: Ta cap layer, and a SiO2 protective layer. CrN is obtained by relatively thick nitriding the surface of Cr. CrN does not oxidize to 1100 ° C. like CrAlN. At temperatures higher than that, a Cr2O3 thermal oxide film is formed on the surface.

  Example 28 is a light emitting structure having micropores of circular openings arranged in a triangular lattice having an Al: TiN main body, a TiNb intermediate layer, an Nb cap layer, and an Nb2O5 protective layer. While the melting point of Ti is 1670 ° C., the melting point of TiN is as high as 3223 ° C. TiN is a covalent substance like SiC, Si3N4, etc., and in general it is difficult to sinter. The compact sintered body of TiN uses a metal powder or a sintering aid such as a metal oxide such as TiO 2, Al 2 O 3, Ta 2 O 5, Nb 2 O 5, or WO 3. The Al: TiN main body of this embodiment is TiN added with 5 w% of Al. In the sintering method, for example, the temperature is raised to 1700 ° C. at a rate of 100 ° C./min under a nitrogen pressure of 50 MPa, held for 30 minutes, and then pressure-sintered at a rate of 100 ° C./min. . Al: TiN has a thermally oxidized Al2O3 film formed on the surface and withstands a temperature of 1100.degree. Al: TiN exhibits light weight and beautiful metallic luster. The melting point of Nb 2 O 3, which is a protective layer, is a stable oxide at 1520 ° C., and can be easily formed by thermal oxidation. Instead of Nb2O3, Al2O3 or Cr2O3 can also be used for the protective layer. As nitrides for light emitting structures, ZrN, TaN, VN, NbN and the like can be used.

  Example 29 is a light emitting structure having micropores of a circular opening arranged in a square lattice shape having a W / SiC body, a TaW intermediate layer, a Ta cap layer, and an Al2O3 protective layer. SiC is used as a refractory or a heating element and is a cheaper material than W. SiC single crystals can also be obtained as substrates for power devices. The melting point of SiC is 2730 ° C., and the thermal expansion coefficient of SiC at room temperature is 4.4 × 10 −6, which is equal to the thermal expansion coefficient of W. Since SiC has a high emissivity and is used as a pseudo black body, it is a suitable material for the main body of the light emitting structure. TaW is a material with no melting point depression and has a melting point of 3200 ° C. The Al2O3 protective layer serves to protect the Ta cap layer from oxidation.

  Example 30 is a light emitting structure having micro apertures of circular openings arranged in a triangular lattice with a BlackAl2O3 body, Mo / Ti intermediate layer, Si: Mo cap layer, and SiO2 protective layer. The black Al2O3 body is the black pigmented alumina described in the sixth embodiment and is a material suitable for the body of the light emitting structure because it has emissivity at infrared wavelengths. The Mo / Ti intermediate layer is formed by sequentially laminating a thin film Ti adhesion layer and a Mo stress relaxation layer on a black Al2O3 main body. During heating MoTi is alloyed. Si: Mo cap layer is made of Mo containing 5 w% of Si. By heating, a SiO2 protective layer is formed on the surface. The melting point of MoTi and black Al 2 O 3 is 2000 ° C. Since the main body is an oxide, an emitter with a long lifetime without thermal degradation can be obtained.

  Example 31 is a light emitting structure having micropores of a circular opening arranged in a square lattice shape having a BlackMgO main body, a Ta / Ti intermediate layer, a Ta cap layer, and a MgO protective layer. The black MgO body is the black pigmented MgO described in the sixth embodiment, and is a material suitable for the main body of the light emitting structure since it has an emissivity at infrared wavelengths. Besides, ceramics such as Ca 2 O 3 and BN can be used. The Ta / Ti intermediate layer is formed by sequentially laminating a thin film Ti adhesion layer and a Ta stress relaxation layer on a black MgO body. During heating Ta / Ti is alloyed. The melting point of MgO is 2850 ° C. Since the body is an oxide, there is no thermal degradation, and because it is a ceramic, a low cost and long life emitter can be obtained. In addition to black MgO, black CaO can also be used as the main body.

  Although the examples of Ti and W are shown as the single intermediate layer in the embodiment described above, Mo, Nb and Hf may also be used. In addition, although the examples of the openings of the micro holes are circular and square, they may be regular polygons.

Some or all of the above embodiments may be described as in the following appendices, but are not limited thereto.
(Supplementary Note 1)
A light emitting structure having a plurality of micropores, wherein the micropores comprise a first material containing a first metal element, and at least a part of the surface other than the micropores is provided with the first metal element Comprises a second material comprising a different second metal element, the emissivity of said first material of light of a wavelength greater than the peak wavelength of the thermal emission spectrum emitted by said light emitting structure A light emitting structure characterized by having a larger emissivity.
(Supplementary Note 2)
The plurality of micropores are periodically arranged, and the size 開口 of the arrangement cycle of the micropores and the depth t of the micropores are 1.08 ≦ Λ / D ≦ 2 with respect to the aperture diameter D of the micropores. And 1 ≦ t / D ≦ 20, and the thickness s of the second material is 1/20 ≦ s / t ≦ 1/2 with respect to the depth t of the micropores. Light emitting structure.
(Supplementary Note 3)
The light emitting structure according to any one of Appendices 1 or 2, wherein the micropores are periodically arranged in a triangular lattice shape or a tetragonal lattice shape, and the aperture shape of the micropores is a circle or a regular polygon.
(Supplementary Note 4)
The first material or the second material has a melting point of 1000 ° C. or more, and the first material is a metal, an alloy, a silicon compound thereof, a boride, a carbide or a nitride thereof, and the second material The light emitting structure according to any one of Appendices 1 to 3, wherein the material is a metal or an alloy.
(Supplementary Note 5)
The metal element of the first material is any one of Cr, Zr, V, Ti, W, Mo, Nb, and Hf, and the metal element of the second material is the metal element of the first material The light emitting structure according to any one of Appendices 1 to 4, which is a different metal element and contains any one of Ta, W, Mo, Nb and Hf.
(Supplementary Note 6)
In addition to the metal element of the first material, it contains at least one element of Fe, Ni, Co, Cu, Al, Si, or contains at least one element of Re, Os, Ir, Pt, Au. 5. The light emitting structure according to 5.
(Appendix 7)
The first material is a silicon compound of WSi2, TaSi, MoSi2, NbSi2, HfSi2, CrSi2, ZrSi2, VSi2, TiSi2, TaB2, W2B5, MoB2, NbB2, HfB2, CrB2, ZrB2, VB2, TiB2, boride, TaC, The light emitting structure according to appendix 4, which is a carbide of WC, MoC, NbC, CrC, ZrC, VC, TiC, or a nitride of TaN, WN, MoN, NbN, CrN, ZrN, VN, TiN.
(Supplementary Note 8)
The at least one element of Cr, Si, Al, V, Zr, Ca, Mg, and Ag is further included in the second material at a concentration of 1 w% to 20 w%. The light emitting structure according to claim 1.
(Appendix 9)
The light emitting structure according to any one of Appendices 5 to 8, further comprising boron in the second material at a concentration in the range of 1 w% to 5 w%.
(Supplementary Note 10)
The surface of the first material or the second material is covered with a protective layer of oxide, and the oxide is a thermal oxide film of the first material or the second material, or the first material The light emission according to any one of Appendices 1 to 9, which is a thermal oxide film containing at least one element of Cr, Si, Al, V, Zr, Ca, Mg, Ag added to the second material Structure.
(Supplementary Note 11)
It has an intermediate layer between the first material and the second material, and the intermediate layer is W, Mo, Nb, Hf, or a metal contained in the first material and the second material A light emitting structure according to any of the preceding claims, which is an alloy comprising an element.
(Supplementary Note 12)
The light emitting structure according to any one of appendices 1 to 11, wherein the first material is in contact with a ceramic substrate or is an oxide material comprising metal impurities or carbon.
(Supplementary Note 13)
The ceramic base material is SiC, Al2O3, SiO2, CaO, MgO or BN, the metal impurity is Co, Cr, Fe, Mn or Ni, and the oxide contains a rare earth, Al, Ga, Si, Ge, The light emitting structure according to appendix 12, which is an oxide material comprising Ca, Mg, Zr or V.
(Supplementary Note 14)
A light emitting structure according to any one of appendices 1 to 13, a heating device for heating the light emitting structure, and a thermophotovoltaic comprising a photoelectric conversion element for photoelectrically converting light from the light emitting structure. A thermal photovoltaic power generation system, which is a power generation system, in which an aperture diameter D of fine holes is controlled to approximately λ0 / 2 with respect to a power generation limit wavelength λ0 of a photoelectric conversion element.
(Supplementary Note 15)
The thermal photovoltaic power generation system according to claim 14, wherein the light emitting structure is heated to a temperature T (600 ° C. ≦ T ≦ 1700 ° C.).
(Supplementary Note 16)
20. A visible light illuminating device comprising: a transparent sealing body obtained by vacuum or rare gas sealing the light emitting structure according to any one of appendices 1 to 13; and a conductive heating device for electrically heating the light emitting structure.
(Supplementary Note 17)
An infrared light source unit including the light emitting structure according to any one of appendices 1 to 13, a measurement cell unit through which an infrared ray from the infrared light source unit is passed and a gas to be detected is introduced, and the measurement cell unit Gas detection device equipped with a detector unit that detects infrared radiation that has passed through.
(Appendix 18)
20. The gas detection device according to appendix 17, further comprising a wavelength selection filter for passing a desired wavelength of infrared rays emitted from the light emitting structure.

The present invention can be applied to applications such as a TPV generator using a photoelectromotive power generation system. Moreover, it is applicable also to applications, such as a gas detector and an incandescent lamp which is visible light illumination.

1 Monocrystalline tungsten
2 rectangular micro holes
11 Light emitting structure
12 Light emitting structure of single crystal tungsten
13 Tantalum cap layer
14 fine holes
Period of 15 micropores
Length L of one side of 16 squares
71 Support stand
72 gas inlet pipe
73 Gas Burner
74 flame opening
75 Light emitting structure (right)
76 Spacer
77 Light emitting structure (left)
78 Thermal insulation support
79 micro hole array
80 support plate
81 PV devices
82 Heat sink
83 Support plate
84 PV devices
85 Heat sink
91 Tungsten single crystal substrate
92 tantalum thin film
93 Photo resist
94 Aluminum thin film
95 Resist for Electron Beam Exposure
96 Electron beam resist mask
97 aluminum mask
98 photoresist mask
99 Tungsten light emitting structure
100 light emitting structure
Light emitting structure of single crystal Cr
102 Ta cap layer
103 pores
104 period Λ x
105 cycles Λ y
106 Opening circle diameter D
107 hole depth t
108 Ta2O5 oxide film
109 Cr2O3 oxide film
110 Support stand
111 methane introduction pipe
112 Air inlet tube
113 Support legs
114 Mixture inlet tube
115 radiation fins
116 PV devices
117 octagonal emitters
118 Burner
119 flame opening
120 insulation board
121 vent
122 inset joint
123 Female Chrome Plate
124 male chrome board
130 Light emitting structure
131 Cr main body
132 Cr2Ta intermediate layer
133 Ta cap layer
134 Cr2O3 Protective Layer
135 Round micro holes
136 triangular lattice period Λ
140 light emitting structure
141 MoSi2 main body
142 TaMoSi2 interlayer
143 Ta cap layer
144 SiO2 protective layer
145 Round micro holes
146 Square grid period Λ
150 light emitting structure
151 Al2O3 base material
152 Cr / Ti coated layer
153 Ta cap layer
154 Al2O3 protective layer
155 Round micro holes
156 square lattice period Λ
157 photoresist mask
158 Cr / Ti layer
159 Cr / Ti lift-off layer
160 Light emitting structure
161 black alumina body
162 Ti interlayer
163 Ta cap layer
164 Al2O3 protective layer
165 Round micro holes
166 square lattice period Λ
170 light emitting structure
171 Er3Al5O12 body
172 Ti intermediate layer
173 Ta cap layer
174 Al2O3 protective layer
175 Round micro holes
176 square lattice period Λ
180 light emitting structure
181 Cr body
182 CrNb interlayer
183 Si: Nb cap layer
184 SiO 2 protective layer
185 Round micro holes
186 square lattice period Λ
190 Infrared light source unit
191 wire
192 heater
193 Light emitting structure
194 Mira
195 wavelength selective filter
196 Measurement cell
197 Detector
198 Rotating chopper
199 Synchronous motor
200 front room
201 back room
202 Heat flow sensor
203 Detection gas inlet
204 Detection gas discharge unit
205 light path
210 Light emitting structure
211 W crystal body
212 AgW cap layer
213 Round micro holes
214 square lattice period Λ
220 center electrode
221 External lead-in
222 base
223 mount
224 valve
225 Internal lead
226 Light emitting structure filament
227 Inert gas
228 insulation

Claims (7)

A light emitting structure having a plurality of circular or regular polygonal micropores, wherein the micropores comprise a first material containing a first metallic element, and at least a portion of the surface other than the micropores. In a thermal emission spectrum emitted when the light emitting structure is heated to a temperature T (300 ° C. ≦ T ≦ 2500 ° C.), including a second material containing a second metal element different from the first metal element The emissivity of the first material is greater than the emissivity of the second material in light of a wavelength greater than the peak wavelength defined as the wavelength with the highest radiation intensity, and the first metal element of the first material Is any one of Cr, Zr, V, Ti, W, Mo, Nb, Hf, or the first material is WSi ₂ , TaSi, MoSi ₂ , NbSi ₂ , HfSi ₂ , CrSi ₂ , ZrSi ₂ , VSi _2, TiSi ₂ made silicon _{compound, TaB 2, W 2 B 5} , MoB 2, NbB 2, HfB 2, CrB 2, ZrB 2, VB 2, TiB 2 becomes borides, TaC, WC, MoC, NbC , CrC, A carbide of ZrC, VC, TiC, or a nitride of TaN, WN, MoN, NbN, CrN, ZrN, VN, TiN,
The light emission structure containing the metal element in which the 2nd metal element of said 2nd material is a metal element different from the metal element of said 1st material, and any one of Ta, W, Mo, Nb, and Hf. The light emitting structure according to claim 1, wherein the fine holes are circular and periodically formed in a square lattice shape or a triangular lattice shape. The surface of the first material or the second material is covered with a protective layer of oxide, and the oxide is a thermal oxide film of the first material or the second material, or the first material The light emitting structure according to claim 1 or 2 , which is a thermal oxide film containing at least one element of Cr, Si, Al, V, Zr, Ca, Mg and Ag added to the second material. It has an intermediate layer between the first material and the second material, and the intermediate layer is W, Mo, Nb, Hf, or a metal contained in the first material and the second material The light emitting structure according to any one of claims 1 to 3 , which is an alloy containing an element. A light emitting structure according to any one of claims 1 to 4 , a heating device for heating the light emitting structure, and a thermal photovoltaic device comprising a photoelectric conversion element for photoelectrically converting light from the light emitting structure. A thermal photovoltaic power generation system, which is a power generation system, wherein an aperture diameter D of the fine holes is controlled to approximately λ0 / 2 with respect to a power generation limit wavelength λ0 of a photoelectric conversion element. A visible light illuminating device comprising: a transparent sealing body obtained by vacuum or rare gas sealing the light emitting structure according to any one of claims 1 to 4 ; and a conductive heating device for electrically heating the light emitting structure. . An infrared light source unit including the light emitting structure according to any one of claims 1 to 4 , a measurement cell unit through which an infrared ray from the infrared light source unit is passed and a gas to be detected is introduced, the measurement cell unit Gas detection device equipped with a detector unit that detects infrared radiation that has passed through.