Semiconducting material and method of manufacturing the same, compact, photoelectric conversion material, and optical filter

Abstract

To provide a semiconducting material that is usable for an SWIR sensor and has light absorptivity in a near-infrared region and a method of manufacturing the same, a compact, a photoelectric conversion material, and an optical filter.SOLUTION: A semiconductor material includes a material which has an energy band gap of 0.7 to 0.95 eV, and is expressed by at least one of Bi2OS2 and Bi2O2S.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a semiconductor material and a manufacturing method thereof, and also to a molded article, a photoelectric conversion material, and an optical filter that contain the semiconductor material. [Background technology]

[0002] By using a SWIR sensor that captures light in the short-wavelength infrared (SWIR) region, it becomes possible to perform new sensing tasks that are not possible with visible light, such as passing it through a semiconductor silicon wafer to check for internal defects or through opaque resin materials to check the contents of a package. However, current SWIR sensors have price issues, such as those made of InGaAs, and environmental issues, such as those made of PbSe, which are barriers to their widespread use.

[0003] On the other hand, chalcogenide-based layered compounds have attracted attention due to their diverse physical properties, and many applications are expected. Non-Patent Document 1 reports that Bi2OS2, a type of chalcogenide-based layered compound, has a band gap of 0.99 eV. Non-Patent Document 2 reports that the band gap is 1.12 eV. Furthermore, Non-Patent Documents 3, 4, and 5 report Bi2O2S with band gaps of 1.31 eV, 1.5 eV, and 1.27 eV. However, while these band gaps are suitable for wavelengths of around 1200 nm or less, they cannot be used as SWIR sensors. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] A. Miura et al., Solid State Communications, 2016, 277,19-22. [Non-patent document 2] H. Yu et al., Applied Surface Science, 2020, 513(145874), 1-11. [Non-patent document 3] Z. Wu et al., Journal of Materials Chemistry A., 2019, 7, 14776-14789. [Non-patent document 4] AL Pacquette et al., Journal of Photochemistry and Photobiology A: Chemistry, 2014, 277, 27-36. [Non-Patent Document 5] F. Wang et al., InfoMat, 2021, 3, 1251-1271. Summary of the Invention [Problem to be solved by the invention]

[0005] Demand for SWIR sensors is expected to grow in the future in fields such as food inspection, semiconductor inspection, identification and classification, and anti-counterfeiting. Accordingly, there is a need to develop new photoelectric conversion materials for SWIR sensors that can absorb SWIR light in the range of around 1300 nm to 1750 nm, replacing conventional semiconductor materials such as InGaAs and PbSe.

[0006] The present disclosure has been made in view of the above background, and aims to provide a semiconductor material that exhibits light absorption in the near-infrared region and that can be used in a SWIR sensor, as well as a method for manufacturing the same, a molded body, a photoelectric conversion material, and an optical filter. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have found that the problems of the present disclosure can be solved in the following aspects, and have thus completed the present disclosure. [1]: The energy band gap is 0.7 to 0.95 eV; A semiconductor material comprising at least one of the composition formula Bi2OS2 and the composition formula Bi2O2S. [2]: The semiconductor material according to [1], which has an X-ray diffraction peak top in the range of 25.3 to 26.5° or 23.8 to 24.9° in an X-ray diffraction pattern obtained by the 2θ / θ scan method of powder X-ray diffraction measurement. [3]: The semiconductor material according to [1] or [2], wherein the half width of the X-ray diffraction peak is 0.05 to 1.2°. [4]: The semiconductor material according to any one of [1] to [3], wherein the crystallite sizes of the composition formula Bi2OS2 and the composition formula Bi2O2S are each independently 20 to 5000 Å. [5]: The semiconductor material according to any one of [1] to [4], which is synthesized by a mechanochemical reaction using a mixture containing raw materials selected from the following (i) or (ii): (i) Composition formula Bi2O3 and composition formula Bi2S3 (ii) Bi, S and the formula Bi2O3 [6]: A step of obtaining a mixture containing a raw material selected from the following (i) or (ii); and synthesizing the mixture by a mechanochemical reaction to form a semiconductor material having an energy band gap of 0.7-0.95 eV. (i) Composition formula Bi2O3 and composition formula Bi2S3 (ii) Bi, S and the formula Bi2O3 [7]: A molded article comprising the semiconductor material according to any one of [1] to [5]. [8]: A photoelectric conversion material comprising the semiconductor material according to any one of [1] to [5]. [9]: An optical filter comprising the semiconductor material according to any one of [1] to [5]. [Effects of the Invention]

[0008] The present disclosure has the excellent effect of providing a semiconductor material that has absorption in the near-infrared region and that can be used in a SWIR sensor, as well as a manufacturing method thereof, a molded body, a photoelectric conversion material, and an optical filter. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a Tauc plot diagram for Example 1 (with post-annealing treatment) and Example 2 (without post-annealing treatment). [Figure 2] XRD patterns of Examples 1 to 9 and Comparative Example 1. [Figure 3] FIG. 1 is a Williamson-Hall plot diagram for Example 1 (with post-annealing treatment) and Example 2 (without post-annealing treatment). [Figure 4] 1 is an SEM image of the semiconductor material of Example 2. [Figure 5] 10 is an SEM image of the semiconductor layer before filtering in Example 10. [Figure 6] 10 is a graph showing the wavelength dependence of absorptance (100-(transmittance T+reflectance R)) in the spin-coated film of Example 10. DETAILED DESCRIPTION OF THE INVENTION

[0010] An example of an embodiment to which the present disclosure is applied will be described below. The present disclosure is not limited to this embodiment, and other embodiments are also included as long as they are consistent with the spirit of the present disclosure. In this specification, a numerical range specified using "to" includes the numerical values ​​written before and after "to". The numerical values ​​specified in this specification are values ​​determined by the methods disclosed in the embodiments or examples. Furthermore, unless otherwise noted, each component may be used independently, either alone or in combination of two or more types.

[0011] 1. Semiconductor materials The semiconductor material of the present disclosure has an energy band gap (hereinafter also referred to as band gap) of 0.7 to 0.95 eV and contains at least one of the composition formulas Bi2OS2 (hereinafter also referred to simply as Bi2OS2) and Bi2O2S (hereinafter also referred to simply as Bi2O2S). That is, it contains the composition formula Bi2OS2, the composition formula Bi2O2S, or a mixture thereof. The semiconductor material of the present disclosure more preferably has a band gap of 0.7 to 0.92 eV and contains at least one of the composition formulas Bi2OS2 and Bi2O2S. From the viewpoint of reducing thermal noise when using a SWIR sensor, the lower limit of the band gap is more preferably 0.75 eV, 0.80 eV, or 0.85 eV. On the other hand, from the viewpoint of preventing noise due to the solar spectrum, the lower limit of the band gap is more preferably 0.75 eV, and the upper limit is more preferably 0.90 or 0.85 eV. The ratio in the case of the mixture is not limited. The content (purity) of Bi2OS2 and Bi2O2S is preferably 35% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 70% by mass or more, 80% by mass or more, 90% by mass or more, even more preferably 95% by mass or more, and may be substantially 100% by mass. Compounds consisting of Bi, O and / or S other than those having the composition formulae Bi2OS2 and Bi2O2S include those having the composition formulae Bi, S, Bi2O3, Bi2S3, Bi9O 0.75 Examples include BiS6 and Bi4O4S3. However, from the viewpoint of obtaining a semiconductor thin film with a band gap of 0.7 to 0.95 eV, the Bi content is preferably low, more preferably less than 5 mol%, even more preferably 3 mol% or less, even more preferably 2 mol% or less, and even more preferably 1 mol%, and Bi may not be substantially contained. In this specification, the term "substantially" is intended to exclude impurities that are inevitably mixed in.

[0012] In 100 mol % (hereinafter also referred to as mol %) of the present semiconductor material, the content (purity) of Bi2OS2 and Bi2O2S is preferably 40 mol % or more, more preferably 60 mol % or more, even more preferably 70 mol % or more, still more preferably 80 mol % or more, even more preferably 90 mol % or more, and may be substantially 100 mol %.

[0013] The compounds represented by the composition formulas Bi2OS2 and Bi2O2S are layered compounds. The composition formula Bi2OS2 is a layered compound having a BiS2 layer made of bismuth atoms (Bi) and sulfur atoms (S) and a BiO layer made of bismuth atoms (Bi) and oxygen atoms (O), with the Bi, O, and S atoms formally represented in a molar ratio of 2:1:2. The composition formula Bi2O2S is a layered compound having a Bi2O2 layer made of bismuth atoms (Bi) and oxygen atoms (O) and an S layer, with the Bi, O, and S atoms formally represented in a molar ratio of 2:2:1. The statement that the composition formula Bi2OS2 "formally has a molar ratio of 2:1:2" means that the actual molar ratio may vary due to minute defects, such as point defects, within the crystal lattice, or impurities, such as ions and atoms, inevitably introduced during the manufacturing process. For example, when analyzing the composition using an electron probe microanalyzer (EPMA) or inductively coupled plasma atomic emission spectroscopy (ICP-AES), the molar ratios of Bi, O, and S atoms may each independently vary by approximately ±10%. The same applies to the molar ratios and their fluctuation ranges in the composition formula Bi2O2S; the molar ratios of Bi, O, and S atoms may each independently vary by approximately ±10%. The layered compounds mentioned above may each independently be single-layer or multi-layer. Like graphite, they can be easily cleaved along their crystal planes.

[0014] The semiconductor material can be confirmed to contain compounds represented by Bi2OS2 and / or Bi2O2S by identifying the crystalline phase contained in the XRD pattern obtained by the 2θ / θ scan method of X-ray diffraction measurement. Specifically, the compounds and crystalline phases can be identified by comparing the obtained XRD pattern with known crystalline phase data. The content of compounds represented by Bi2OS2 and / or Bi2O2S in the semiconductor material can be determined by Rietveld analysis or the WPPF method. These XRD patterns can also be analyzed using analysis software such as "PDXL2" manufactured by Rigaku Corporation.

[0015] The energy band gap is the valence band (E v ) to the conduction band (E c ) is the difference in energy between the wavelengths of light emitted from the semiconductor material and the wavelengths of light emitted from the semiconductor material. By using this semiconductor material with an energy band gap of 0.7 to 0.95 eV, light in the short-wavelength infrared (SWIR / Short-Wavelength InfraRed) region can be absorbed. In other words, since this semiconductor material can absorb SWIR light, it is particularly suitable as a photoelectric conversion material.

[0016] The band gap of this semiconductor material can be calculated from the Tauc plot. The semiconductor material to be measured is mixed with a standard sample, KBr, to prepare a measurement sample. Diffuse reflectance spectroscopy is performed on this sample, and the diffuse reflectance spectrum (horizontal axis: wavelength (nm), vertical axis: relative reflectance r ∞ The resulting diffuse reflectance spectrum is expressed as f(r ∞ )=(1-r ∞ ) 2 / 2r ∞ According to the Kubelka-Munk function f(r ∞ ) Next, the obtained spectrum (horizontal axis: wavelength (nm), vertical axis: f(r ∞ )) is plotted on a Tauc plot (horizontal axis: electron energy hν, vertical axis: (hνα) 1 / r ) where h is Planck's constant (J s) and ν is the frequency of light (s -1 ) where α is the absorption coefficient, and f(r∞ ) can be used instead. r is a value determined by the type of transition, and for this semiconductor material, which is a direct transition type, r = 1 / 2 is used. From the above, the horizontal axis is hν and the vertical axis is (hνf(r ∞ )) 2 ) can be obtained. In the above Tauc plot, tangent lines are drawn to the baseline of the spectrum and to the rising part of the absorption, and the value on the horizontal axis at the intersection of the tangent lines is the band gap value. Here, the baseline refers to the flat or linear part that exists before the rising part of the absorption.

[0017] Short-wavelength infrared (SWIR) light refers to light with a wavelength of 1000 to 2500 nm. The applicable SWIR band can be designed depending on the application, but when used in a SWIR sensor, a wavelength of 1300 to 2000 nm is more preferable. A more preferable lower limit of the wavelength is 1350 nm or 1380 nm, and a more preferable upper limit of the wavelength is 1750 nm. When used in an environment where sunlight is incident, a wavelength of 1300 to 1650 nm is preferable, since the low intensity of the sunlight spectrum reaching the ground reduces malfunction. For SWIR sensor applications, wavelengths of 1300 to 1750 nm are suitable for detecting transmission through plastic containers and silicon wafers, and for detecting the presence of plastic, metal, and rubber. A wavelength around 1450 nm is also suitable for moisture detection.

[0018] The compound represented by the composition formula Bi2OS2 contained in this semiconductor material has a lattice constant (hereinafter also referred to as lattice constant c) in the stacking direction of the layered structure in the crystal structure (hereinafter also referred to as the c-axis direction) of preferably 13.620 Å, and may also be 13.650 Å or 13.700 Å. The upper limit of the lattice constant c is preferably 13.795 Å, and may also be 13.792 Å or 13.790 Å.

[0019] Furthermore, the compound represented by the composition formula Bi2OS2 contained in the present semiconductor material has a lattice constant (hereinafter also referred to as lattice constant a) in the in-plane direction (hereinafter referred to as a-axis direction) of preferably 3.955 Å, and may also be 3.962 Å, 3.963 Å, or 3.964 Å. The upper limit of the lattice constant c is preferably 3.968 Å, and may also be 3.967 Å or 3.966 Å.

[0020] The compound represented by the composition formula Bi2O2S contained in the present semiconductor material preferably has a lattice constant in the stacking direction of the layered structure in the crystal structure (hereinafter also referred to as the c-axis direction) of 11.950 Å to 12.400 Å. The lower limit of the lattice constant is more preferably 12.000 Å, even more preferably 12.050 Å, and even more preferably 12.100 Å. The upper limit of the lattice constant is more preferably 12.300 Å, and even more preferably 12.250 Å.

[0021] The compound contained in this semiconductor material and represented by the composition formula Bi2O2S preferably has a lattice constant in the in-plane direction (hereinafter referred to as the a-axis direction) of 3.800 to 3.870 Å, more preferably 3.830 to 3.865 Å, and even more preferably 3.850 to 3.860 Å. Bi2O2S has two crystal axes (a-axis and b-axis) in the in-plane direction, but the one with the smaller lattice constant is treated as the a-axis direction and the one with the larger lattice constant is treated as the b-axis direction.

[0022] As a result of extensive research, the inventors have found that an energy band gap of 0.7 to 0.95 eV can be easily achieved by including at least one of the composition formulas Bi2OS2 and Bi2O2S and having a lattice constant within the above range. The lattice constants a and c can be determined from the XRD pattern obtained by powder X-ray diffraction (XRD). For example, they can be calculated by performing analysis using the WPPF (Whole Powder Pattern Fitting) method using XRD analysis software such as PDXL2 (manufactured by Rigaku Corporation).

[0023] The present semiconductor material may be formed by any of a variety of processes, including raw material components (e.g., Bi, S, Bi2O3, Bi2S3), by-products (e.g., Bi9O 7.5 The total content of BiOS is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0024] Bi2OS2 has an X-ray diffraction peak attributable to the (004) plane in the range of 25.3 to 26.5°. Bi2O2S has an X-ray diffraction peak attributable to the (011) plane in the range of 23.8 to 24.9°. That is, in the X-ray diffraction pattern obtained by the 2θ / θ scan method, this semiconductor material has an X-ray diffraction peak top in the range of 25.3 to 26.5° or 23.8 to 24.9°. Here, peak top refers to the position showing the maximum value in the target X-ray diffraction peak.

[0025] In order to reduce the crystallite interfaces and non-uniform distortion of the crystals, the present semiconductor material preferably has an X-ray diffraction pattern in which the half-width of the Bi2OS2 peak and the half-width of the Bi2O2S peak are each independently 1.2° or less. Furthermore, the upper limits of the half-widths of the peaks within the above ranges are each independently more preferably 1.0° or less, even more preferably 0.7° or less, and even more preferably 0.4° or less. The lower limits of the half-widths of the peaks within the above ranges are not limited, but can be, for example, 0.05°. The lower limits may be 0.075° or 0.1°.

[0026] The shape of this semiconductor material can be designed as desired. However, since it is a layered compound, scale-like particles are preferred for powders. The average particle size can be selected appropriately depending on the application. For example, the average particle size can be approximately 0.1 to 50 μm, and the average thickness can be approximately 0.05 to 10 μm. Nanoparticles of 1 to 100 nm can also be used. The use of nanoparticles with these particle sizes can improve the dispersion stability of dispersions, the smoothness of molded bodies and thin films, and utilize quantum effects. The average particle size can also be approximately 50 to 200 μm. The average particle size and thickness are determined by observing the semiconductor material with a scanning electron microscope (SEM) at 10,000x magnification and averaging the diameters and thicknesses of 100 particles measured on the observed image. The average particle size is calculated by taking the maximum length of each particle as the particle diameter. When using plasmon resonance particles or quantum dots, the particle size can be adjusted by grinding or other methods.

[0027] The crystallite size of the (004) plane of the present semiconductor material can be appropriately designed, but from the viewpoint of carrier transport, it is preferably 20 to 5000 Å, more preferably 100 to 4000 Å, and even more preferably 200 to 3000 Å.

[0028] The inhomogeneous strain of the crystal of the semiconductor material can be appropriately designed, but from the viewpoint of carrier transport, it is preferably 2% or less, more preferably 1% or less, and even more preferably 0.5% or less. In particular, the inhomogeneous strain of the (00x) plane, such as the (001) plane or the (002) plane corresponding to the c-axis direction, is preferably 0.001% or less.

[0029] The crystallite size and crystal inhomogeneity of the Bi2OS2 and Bi2O2S compositions can be determined from powder X-ray diffraction (XRD) patterns. Specifically, they can be calculated from a Williamson-Hall plot using the diffraction angle and full width at half maximum (hereinafter referred to as FWHM) of the diffraction peak of each crystal plane in XRD measurements. The calculation method is described below. First, the diffraction angle (angle of the peak top) and half-width of each diffraction peak in the XRD pattern are determined. Using the determined diffraction angle and half-width, a plot (horizontal axis: sinθ / λ, vertical axis: (Δ2θ)cosθ / λ) is created. Here, θ is the diffraction angle (°) of each diffraction peak, Δ2θ is the half-width (°) of each diffraction peak, and λ is the wavelength (Å) of the X-rays used in the XRD measurement. A regression line is drawn for this plot using the least squares method, giving (Δ2θ)cosθ / λ=K(D -1 +2η sinθ / λ), the inhomogeneous strain η of the crystal is calculated from the slope of the regression line, and the crystallite size D (Å) is calculated from the intercept. K is the Scherrer constant. When calculating the crystallite size and non-uniform distortion of the crystal for a specific crystal plane, each diffraction peak is indexed, and a Williamson-Hall plot is created from the diffraction peaks of each crystal plane to calculate these.

[0030] 2. Manufacturing methods for semiconductor materials An example of a method for manufacturing the semiconductor material of this embodiment is described below. However, the semiconductor material of this embodiment only needs to have an energy band gap of 0.7 to 0.95 eV and contain at least one of the composition formulas Bi2OS2 and Bi2O2S, and can be manufactured by arbitrarily combining it with known manufacturing methods or by appropriately changing the manufacturing conditions. Suitable methods for manufacturing this semiconductor material include solid-phase methods, liquid-phase methods, mechanochemical methods, vapor deposition methods, chemical vapor deposition (CVD) methods, and combinations of these methods.

[0031] The solid-state method is a method of producing a target material in a solid phase, using atomic diffusion due to heating as the main driving force. One example of a solid-state method is a method of mixing Bi2S3 and Bi2O3, or Bi, S, and Bi2O3, in a stoichiometric ratio, sealing the mixture in a quartz glass tube under vacuum, and heating it at 300 to 400°C. The energy band gap of the resulting semiconductor material can be adjusted by, for example, the reaction time, reaction temperature, reaction atmosphere, number of heating cycles, or the ratio of raw materials added, or by a combination of any two or more of these.

[0032] The mechanochemical method is a method for producing a target substance using mechanical energy as the main driving force, and is characterized by not requiring high temperature or high pressure conditions. When producing powders as semiconductor materials, the mechanochemical method is preferable from the viewpoints of simplicity and energy cost. In particular, the mechanochemical method is preferable for the present semiconductor material because it prevents thermal decomposition during synthesis and improves purity.

[0033] An example of a mechanochemical manufacturing method will be described below. However, the manufacturing method of the semiconductor material of the present disclosure is not limited to the manufacturing method described below. For example, the semiconductor material can be manufactured by obtaining a mixture containing raw materials selected from the following (i) or (ii) and subjecting this mixture to a mechanochemical reaction. (i) Composition formula Bi2O3 and composition formula Bi2S3 (ii) Bi, S and the formula Bi2O3 The case of (i) will be explained below, and the case of (ii) can be produced in the same manner.

[0034] First, a mixture containing Bi2O3 and Bi2S3 is obtained as raw materials (step a). Bi2O3 and Bi2S3 may be used as raw materials, and these may contain other components (such as components that may be unavoidably contained) within the scope of the present disclosure. In step a, Bi2O3 and Bi2S3 are mixed in a dry state taking into account the stoichiometric ratio. Step a is usually performed simultaneously with step b, which will be described later. In step a, the mixing ratio of Bi2O3 to Bi2S3, "Bi2S3 (mol) / Bi2O3 (mol)," is preferably 1.2 or more, more preferably 1.4 or more, even more preferably 1.6 or more, and particularly preferably 1.8 or more, from the viewpoint of obtaining a semiconductor material containing Bi2OS2 and having a predetermined band gap. It is also preferably 5.0 or less, more preferably 4.0 or less, even more preferably 3.5 or less, even more preferably 3.0 or less, and particularly preferably 2.5 or less. A mixing ratio of 2 is particularly preferred. From the viewpoint of obtaining a semiconductor material containing Bi2O2S and having a predetermined band gap, the above mixing ratio is preferably 0.3 or more, more preferably 0.35 or more, even more preferably 0.4 or more, and particularly preferably 0.45 or more. It is also preferably 0.65 or less, more preferably 0.60 or less, and even more preferably 0.55 or less. A mixing ratio of 0.5 is particularly preferred. Before the mixing in step a, a pretreatment step may be performed in which the raw materials are pulverized at room temperature using, for example, an agate mortar (for 3 to 60 minutes). Furthermore, in step a, in order to improve uniformity or adjust particle size, the raw materials may be mixed at room temperature using, for example, an agate mortar (for 30 to 60 minutes) after mixing.

[0035] Commercially available Bi2O3 and Bi2S3 may be used. The average particle diameter D50 of Bi2O3 and Bi2S3 is, for example, 50 nm to 1 mm. From the viewpoint of efficient synthesis reaction, a smaller particle diameter is preferable. From the viewpoint of uniformity, a small particle diameter and a narrow particle size distribution are preferable. The average particle diameter D50 refers to the particle diameter that is 50% cumulative from the smallest diameter side in the volume-based particle size distribution. Examples of commercially available products include Bi2O3 (manufactured by Kojundo Chemical Research Institute, BI005PB, average particle diameter 20 μm) and Bi2S3 (manufactured by Strem Chemicals).

[0036] Next, the prepared mixture is subjected to a mechanochemical reaction to synthesize a semiconductor material having an energy band gap of 0.7 to 0.95 eV (step b). The energy band gap of the resulting semiconductor material can be adjusted, for example, by adjusting the rotation speed, rotation time, bead diameter, or the ratio of raw materials added in the mechanochemical process of step b, or by a combination of any two or more of these. In step b, a semiconductor material containing at least one of the composition formulas Bi2OS2 and Bi2O2S is obtained from the mixture prepared in step a by a mechanochemical reaction.

[0037] Mechanochemical reactions are chemical reactions such as crystallization, solid-solution reactions, and phase transition reactions that utilize high localized energy generated by physical energies such as powder crushing, collision, friction, and compression. The raw materials, Bi2O3 and Bi2S3, are subjected to mechanochemical processing, such as by collision of a dispersion medium, which applies mechanical energy from multiple directions, resulting in pulverization, changes in crystal structure, and activation of the particle surface, resulting in a chemical reaction that synthesizes the semiconductor material. The environmental conditions for the mechanochemical reaction are not particularly limited; it can be carried out at room temperature in air, under a nitrogen atmosphere, or in an inert gas such as argon. Furthermore, the reaction can be carried out at high or low temperatures, or under pressure or reduced pressure, as needed.

[0038] The apparatus for performing the mechanochemical treatment is not particularly limited, and examples thereof include grinding / dispersing machines such as bead mills, ball mills, planetary ball mills, vibration mills, turbo mills, and disk mills. Alternatively, a method of applying mechanical energy by placing powder in a container and rotating a rotor or blade can be used, and examples include Nobilta and Mechanofusion from Hosokawa Micron Corporation. Among these, ball mills are preferred. Examples of beads used in ball mills include zirconia beads, quartz glass beads, soda-lime glass beads, alumina beads, and mixtures thereof. From the viewpoint of preventing the incorporation of impurities, ceramics such as zirconia beads and alumina beads are preferred.

[0039] When mechanochemical treatment is performed using a ball mill, the rotation speed of the ball mill is, for example, about 100 to 2,000 rpm, and may be in the range of 200 to 1,500 rpm or 300 to 1,000 rpm. The treatment time is, for example, about 200 to 5,000 minutes, or may be about 300 to 1,000 minutes. The size of the beads used in the ball mill is, for example, a diameter of 0.5 to 15 mm, preferably 1 to 10 mm, and more preferably 2 to 8 mm. By setting the diameter to 2 to 8 mm, the collision energy can be maintained appropriately, which not only enhances the reactivity of the mechanochemical reaction but also suppresses the generation of impurities.

[0040] In the mechanochemical reaction, a solvent may be added to form a paste, if necessary. When a wet reaction is performed using a solvent, known organic solvents can be used, but nonaqueous solvents are preferred to produce a highly pure semiconductor material. Specific examples include hydrocarbon solvents such as hexane, octane, toluene, and xylene; halogenated hydrocarbon solvents such as chloroform, chlorobenzene, and o-bromotoluene; alcohol solvents such as 1-propanol, 1-butanol, and ethylene glycol; ketone solvents such as methyl isobutyl ketone and cyclohexanone; and ester solvents such as ethyl acetate, isoamyl acetate, and propylene glycol monomethyl ether acetate. Two or more dispersion media can also be used in combination. After step b), a filtration or centrifugation step may be carried out to remove coarse particles. The progress of the reaction can be confirmed by identifying the diffraction peaks attributable to the semiconductor material in the XRD pattern. Heating is not required, but heating is not excluded. This allows the reaction to proceed more efficiently than in a solution. Through the above process, a semiconductor material having a layered crystal structure and containing at least one of the composition formulas Bi2OS2 and Bi2O2S is obtained.

[0041] A suitable example of a liquid phase method is hydrothermal synthesis. Hydrothermal synthesis is a synthesis method that uses high-temperature pressurized hot water as a reaction field, and synthesizes the target substance at a relatively low temperature (approximately 100°C to 400°C) compared to solid phase methods. An example of a hydrothermal synthesis production method is a method in which thiourea (SC(NH2)2) (95 mol%) and Bi2O3 (5 mol%) are added to and mixed with an aqueous NaOH solution, and the solution is heated at 300°C for 4 hours to obtain Bi2OS2 (J. Chen et al., Chemical Engineering Journal, 2021, 420, 127700, etc.). Another suitable example of a liquid-phase method other than hydrothermal synthesis is the reaction of sodium nitrate pentahydrate (Bi(NO3)3·5H2O) and thiourea as Bi and S sources, respectively, in a KOH·NaOH aqueous solution at room temperature to obtain Bi2O2S (Chitara B et al., Nanoscale., 2020, 12(30), 16285-16291.).

[0042] 3. Molded body The molded article of the present disclosure includes the semiconductor material of the present disclosure. Examples of the molded article include molded articles in desired shapes, such as films, sheets, pellets, and plates. The energy band gap of the molded article of the present disclosure is preferably 0.7 to 0.95 eV, more preferably 0.7 to 0.92 eV. From the viewpoint of reducing thermal noise when using a SWIR sensor, the lower limit of the band gap is more preferably 0.75 eV, 0.80 eV, or 0.85 eV. On the other hand, from the viewpoint of preventing noise due to the solar spectrum, the lower limit of the band gap is more preferably 0.75 eV, and the upper limit is more preferably 0.90 or 0.85 eV. Furthermore, in the X-ray diffraction pattern of the molded article of the present disclosure, the X-ray diffraction peak preferably has a peak top in the range of 25.3 to 26.5° or 23.8 to 24.9°.

[0043] The compact of the present disclosure can be formed, for example, from a powdered semiconductor material through a process such as pressure molding. Alternatively, a powdered semiconductor material may be blended with other components and then subjected to a coating process or the like to produce a compact. More specifically, examples of such compacts include compacts obtained by pressure molding powdered Bi2OS2, compacts obtained by pressure molding powdered Bi2O2S, and compacts obtained by pressure molding a mixture of these. Such compacts can be produced, for example, by applying pressure at a pressure of 100 to 500 MPa for 1 minute to 2 hours. Another example of such compacts includes compacts obtained by pressure molding a mixture of at least one of Bi2OS2 and Bi2O3 and another component (e.g., a composition formula of Bi2S3). The density of the resulting compact can be improved by heating to 100 to 400°C during pressure molding.

[0044] Furthermore, a molded body may be obtained by applying a composition consisting of a dispersion or solution containing the semiconductor material Bi2OS2 of the present disclosure and other components to a substrate and forming the molded body. Examples of other components include solvents, resins, dopants, dispersants, and additives. Using a resin as a binder can improve moldability. Adding a dopant can adjust the electrical conductivity of the semiconductor material. Adding a dispersant can prevent aggregation and coarsening of the semiconductor material, and promote dispersion and stabilization. Examples of additives include antistatic agents, flame retardants, plasticizers, antioxidants, ion scavengers, UV absorbers, and thermal conductive agents.

[0045] Many dispersants are composed of a moiety that adsorbs to particles and a moiety that stabilizes dispersion. The dispersant used in the present disclosure preferably contains a compound having a phosphate group or phosphoric acid. When the dispersant contains a compound having a phosphate group or phosphoric acid, adsorption to the particle surface is promoted compared to when the dispersant does not contain phosphoric acid, and the dispersion stability of the dispersion and the smoothness of the molded product can be improved.

[0046] Known organic solvents can be used as the dispersion medium, but a solvent capable of uniformly dispersing the semiconductor material is preferred to form a uniform molded body. Specific examples include, but are not limited to, hydrocarbon solvents such as hexane, octane, toluene, and xylene; halogenated hydrocarbon solvents such as chloroform, chlorobenzene, and o-bromotoluene; alcohol solvents such as 1-propanol, 1-butanol, and ethylene glycol; ketone solvents such as methyl isobutyl ketone and cyclohexanone; and ester solvents such as ethyl acetate, isoamyl acetate, and propylene glycol monomethyl ether acetate. Among these, 1-propanol and 1-butanol are preferred. Two or more dispersion media can also be used in combination.

[0047] The particle size of the semiconductor material can be appropriately designed depending on the application, but from the viewpoint of forming a semiconductor layer with high smoothness, nanoparticles (for example, a Z-average particle size of 2 to 250 nm as determined by the cumulant method) are preferred. By making the particle size 2 to 50 nm, it is possible to increase the specific surface area and adjust the band gap, which is expected to be applied to next-generation electronic devices. Furthermore, from the viewpoint of maintaining good dispersibility in the dispersion liquid and semiconductor layer, a particle size of 50 nm to 1 μm is preferred, and from the viewpoint of ease of handling, a particle size of 1 to 200 μm is preferred. The semiconductor layer can be obtained by applying the coating by spin coating, for example, and removing the solvent by heating and drying. To improve the crystallinity, an annealing treatment may be further carried out at, for example, 200 to 500°C, or 200 to 450°C.

[0048] When forming a semiconductor layer, the shape of the semiconductor layer and the proportion of the present semiconductor material in the semiconductor layer can be designed appropriately depending on the application. On the other hand, in applications involving carrier and energy transport such as thermal conduction, electrical conduction, and photoelectric conversion, the content of the present semiconductor material in the semiconductor layer is preferably at least 60 mass%, more preferably at least 80 mass%, and even more preferably at least 90 mass%, from the viewpoint of effectively utilizing the properties of the present semiconductor material. There is no particular upper limit to the content of the present semiconductor material, but it may be 100 mass% or less. When a dispersion is applied by spin coating to form a molded body, a semiconductor layer of any desired thickness can be obtained by adjusting the coating conditions and concentration. Here, concentration refers to the ratio of the total solids (meaning components other than those that volatilize due to evaporation of solvents, etc.) to the total mass of the dispersion. The thickness of the resulting spin-coated film can be adjusted appropriately depending on the application, but from the viewpoint of smoothness and uniformity of the semiconductor layer, a film thickness of 1 μm or less formed by a single spin coating is preferred. A second coating can also be applied and laminated on top of the dried coating film.

[0049] The molded article of the present disclosure is suitable for use as a photoelectric conversion material, an electronic device such as an optical filter, etc. It may also be used as a target for forming a semiconductor thin film.

[0050] 4. Photoelectric conversion materials and optical filters The photoelectric conversion material of the present disclosure includes the present semiconductor material. The present photoelectric conversion material can be used, for example, as a material constituting a photoelectric conversion member disposed between an anode and a cathode. One embodiment of the photoelectric conversion material of the present disclosure includes a compact (pellet) obtained by compressing powder of the present semiconductor material. In another embodiment, the present photoelectric conversion material may be a molded body, such as a semiconductor layer, formed on a substrate. The molded body can be formed from the present semiconductor material alone or a mixture of the present semiconductor material with other components. Examples of other components include resins, semiconductor materials other than the present semiconductor material, dopants, and various additives. The molded body may also be a laminate with other layers. When a dopant is added to adjust the electrical conductivity of the present photoelectric conversion material, it can be added during the production of the semiconductor material, during the production of the molded body, or at any time after the production of the molded body. The type of substrate can be selected appropriately depending on the application. Examples include resin films, glass, quartz, silicon, carbon, ceramics, and metals. Building materials such as cement and concrete can also be used as the substrate.

[0051] The optical filter of the present disclosure includes the semiconductor material. The optical filter according to one embodiment of the present disclosure may be a compact (pellet) obtained by compressing a powder of the semiconductor material by pressing. In another embodiment, the optical filter is obtained as a molded product such as a film or plate in which the semiconductor material is dispersed in a resin that functions as a binder. If necessary, a molded product such as a film or plate may be formed on a substrate. An optical filter containing the semiconductor material can provide an optical filter that absorbs near-infrared light (1300 to 1750 nm). The optical filter can be suitably used as an ND filter that attenuates light with wavelengths of 1300 to 1750 nm or shorter, or as a long-pass filter that selectively transmits light with wavelengths of 1300 to 1750 nm or longer. Suitable examples of the substrate are the same as those for the photoelectric conversion member. [Example]

[0052] The present disclosure will be described below based on examples, but the present disclosure is not limited thereto. In the examples, "parts" and "%" represent "parts by mass" and "% by mass", respectively.

[0053] A. Synthesis of semiconductor materials Example 1 2.44 g of Bi (manufactured by Kojundo Chemical Laboratory Co., Ltd.) and 0.56 g of S (manufactured by Kojundo Chemical Laboratory Co., Ltd.) were prepared and ground and mixed in an agate mortar in an argon atmosphere for 30 minutes as a pretreatment. This mixed powder was placed in a quartz glass tube with one end closed, and the pressure inside the quartz tube was reduced to 1 × 10 using a tabletop turbomolecular pump (manufactured by Osaka Vacuum Equipment Co., Ltd., FTC70FR013) as a vacuum pump. -3 The pressure was adjusted to 100 Pa or less. The quartz tube was sealed while maintaining the pressure using a Kinoshita Blue Hand Burner (Kinoshita Rika Kogyo, KBSS-500). After that, heat treatment (annealing treatment) was carried out at 400 °C for 10 hours to obtain Bi2S3.

[0054] Then, 93.75 parts of zirconia balls (4 mm) were placed in an 80 mL zirconia pot (manufactured by Fritsch Japan Co., Ltd.), and then 4.30 parts (66.67 mol%) of the obtained Bi2S3 and 1.95 parts (33.33 mol%) of Bi2O3 (manufactured by Kojundo Chemical Laboratory Co., Ltd., BI005PB, average particle diameter D50: 20 μm) were placed in the pot.

[0055] The zirconia pot was placed in a planetary ball mill (Fritsch Japan, PL-7) and planetary-stirred. Synthesis was carried out by mechanochemical reaction at room temperature in an argon atmosphere at 500 rpm for 9 hours. The powder was then compacted into a 10 mm diameter disk by uniaxial pressing using a press (Masada Manufacturing, MTP-10HP) at 300 MPa for 1 minute. To improve crystallinity, the powder sample was post-annealed at 400 °C for 10 hours in vacuum. The pellet was then crushed in an agate mortar to obtain a powder (semiconductor material) with an average particle size of 5.0 μm. Powder X-ray diffraction (XRD), described below, confirmed the formation of a powder semiconductor material containing Bi2OS2.

[0056] Examples 2 to 7 Powdered semiconductor materials were synthesized and identified in the same manner as in Example 1, except that the conditions were changed as shown in Table 1. "-" for annealing treatment indicates that no post-annealing treatment was performed.

[0057] Example 8 68.82 parts (66.67 mol%) of Bi2S3 obtained by the method described in Example 1 and 31.18 parts (33.33 mol%) of Bi2O3 similar to that in Example 1 were ground and mixed in an agate mortar in an argon atmosphere for 30 minutes. A press (MTP-10HP, manufactured by Masada Seisakusho) was then used to produce a powder compact. 100 parts of this powder compact were placed in a quartz glass tube with one end closed, and the pressure inside the quartz tube was reduced to 1 × 10 using a tabletop turbomolecular pump (FTC70FR013, manufactured by Osaka Vacuum Equipment Works, Ltd.) as a vacuum pump. -3 The pressure was adjusted to less than Pa. The quartz tube was vacuum sealed while maintaining the pressure using a Kinoshita type blue hand burner (KBSS-500, manufactured by Kinoshita Rika Kogyo). The above-mentioned grinding and mixing, powder compact preparation, and vacuum sealed tube were carried out, followed by heat treatment at 400°C for 10 hours, removal of the powder compact, and grinding. This series of steps was repeated three times. In other words, the heat treatment was carried out for a total of 30 hours, and the final ground powder was obtained. The heating rate during the heat treatment was 50°C / h. XRD confirmed that a powder semiconductor material containing Bi2OS2 was obtained.

[0058] Example 9 Powdered semiconductor materials were synthesized and identified in the same manner as in Example 8. However, the raw materials were changed to those shown in Table 1, and the heating rate was set to 160° C. / h.

[0059] (Comparative Example 1) Powdered semiconductor materials were synthesized and identified in the same manner as in Example 8. However, the raw materials were changed to the conditions shown in Table 1, the heating rate was 200°C / h, and the synthesis process was repeated twice.

[0060] B. Evaluation of semiconductor materials The composition formula Bi2OS2 or Bi2O2S contained in each example and comparative example was identified, and the content (purity) of the compound was calculated by the following method. The results are shown in Table 1.

[0061] <Analysis of Compounds> The semiconductor materials of Examples 1 to 9 and Comparative Example 1 (hereinafter referred to as each Example) were subjected to powder X-ray diffraction measurement by the 2θ / θ scan method using an X-ray diffraction (XRD) device (Mini Flex, manufactured by Rigaku Corporation). The XRD measurement conditions were CuKα characteristic X-ray (λ=1.5418 Å), tube voltage 40 kV, tube current 15 mA, sampling step 0.01°, scan speed 0.7° / min, and 2θ range of 5 to 120°. The crystalline phases contained were identified from the obtained XRD patterns, and it was confirmed that compounds represented by the composition formula Bi2OS2 and / or Bi2O2S were contained. In addition, the mole percent of the compounds represented by the composition formula Bi2OS2 and / or Bi2O2S contained in Examples 1 to 9 and Comparative Example 1 was calculated from the ratio of each crystalline phase determined by Rietveld analysis, and this value was used as the content (purity). The mass percent was calculated from mole percent using the atomic weight of each atom.

[0062] <Band gap energy (BG) measurement> A measurement sample was prepared by mixing 1 g of each powder with 30 g of KBr, a standard sample. The diffuse reflectance spectrum of each powder was measured using a spectrophotometer (Hitachi High-Tech U-4000). The resulting spectrum was plotted on a Tauc plot (horizontal axis: hν, vertical axis: (hνf(r ∞ )) 2 The band gap energy was calculated by converting the band gap energy of each sample into a tangent line, drawing tangent lines to the baseline and the rising edge of the absorption peak, and taking the value on the horizontal axis at the intersection of the tangent lines as the band gap energy. The band gap energy of each sample was evaluated according to the following criteria: +++: Band gap energy is 0.74 eV or more and 0.84 eV or less. ++: Band gap energy is 0.72 or more and 0.87 eV or less (however, does not fall under the above +++ category). +: Band gap energy is 0.70 or more and 0.95 eV or less (however, does not fall under either +++ or ++ above). NG: Does not fall under any of the above +++, ++, or +. In addition, the band gap energy is also classified into A to C for each band. A: Band gap energy is 0.70 eV or more and less than 0.80 eV. B: Band gap energy is 0.8 or more and less than 0.90 eV. C: Band gap energy is 0.90 or more and 0.95 eV or less. D: None of the above A, B, or C applies.

[0063] <Crystalline state analysis (half-width, crystallite size, non-uniform strain)> The half-width, crystallite size, and crystalline inhomogeneity of the XRD pattern for each example were determined using the following method. Powder X-ray diffraction measurements were performed on the powders obtained in each example using the X-ray diffraction (XRD) apparatus (Mini Flex, manufactured by Rigaku Corporation). Peaks representing the compounds represented by the formulas Bi2OS2 and Bi2O2S were identified from the resulting XRD patterns, and the half-widths of the corresponding peaks in the 25.3-26.5° or 23.8-24.9° range were calculated. Crystallite size and crystalline inhomogeneity were determined from Williamson-Hall plots using the peaks of the compounds represented by the formulas Bi2OS2 or Bi2O2S in the 5-80° range. The Scherrer constant K was set to 0.9.

[0064] The XRD peak half-width, crystallite size, and inhomogeneous strain were evaluated according to the following criteria. The inhomogeneous strain was calculated from the slope of the regression line as the value of the inhomogeneous strain η × 100 (%) of the crystal. (XRD peak half-width) ++++: Peak half-width is 0.1° or more and 0.4° or less. +++: Peak half-width is greater than 0.4° and less than 0.7°. ++: Peak half-width is more than 0.7° and less than 1.2°. +:Over 1.2°. *: Less than 0.1°. (crystallite size) ++++: Crystallite size is 200 Å or more and 3000 Å or less. +++: Crystallite size is 100 Å or more and less than 200 Å. ++: Crystallite size is 20 Å or more and less than 100 Å. +: Less than 20 Å. *: Over 3000Å, under 5000Å. **:Over 5000Å. (non-uniform distortion) ++++: Non-uniform distortion is less than 0.5% (including 0%). +++: Non-uniform distortion is 0.5% or more and less than 1.0%. ++: Non-uniform distortion is 1.0% or more and less than 2.0%. +: Non-uniform distortion is 2.0% or more.

[0065] <Evaluation 1: Absorption at 1400 nm> The powder obtained in each example was subjected to diffuse reflectance spectrum measurement, and the obtained spectrum was plotted on a Tauc plot (horizontal axis: hν, vertical axis: (hνf(r ∞ )) 2 )) was converted to the Tauc plot. A tangent was drawn to the baseline of this Tauc plot by the least squares method, and the tangent and the spectrum (hνf(r ∞ )) 2 If the difference in the values ​​was 0.02 or more, it was judged as GOOD, and if it was less than 0.02, it was judged as NG.

[0066] [Table 1]

[0067] <Analysis of crystalline state (lattice constant a and lattice constant c)> X-ray diffraction was performed on the semiconductor materials of Examples 1 to 9 using the above-mentioned X-ray diffraction (XRD) device (Mini Flex, manufactured by Rigaku Corporation). The obtained XRD patterns were analyzed by the WPPF method using XRD analysis software (PDXL2, manufactured by Rigaku Corporation), and the lattice constants a and c were calculated. The results are shown in Table 2.

[0068] [Table 2]

[0069] Figure 1 shows the Tauc plots for Example 1 (with post-annealing treatment) and Example 2 (without post-annealing treatment). As shown in the figure, Example 2 without post-annealing treatment had a band gap of 0.82 eV, while Example 1 with post-annealing treatment had a BG of 0.77 eV, confirming that the band gap narrows due to post-annealing treatment.

[0070] Figure 2 shows the XRD patterns of Examples 1 to 9. As shown in the figure, it was confirmed that the compound represented by the composition formula Bi2OS2 had a diffraction peak top in the range of 25.3 to 26.5°, and the compound represented by the composition formula Bi2O2S had a diffraction peak top in the range of 23.8 to 24.9°.

[0071] Figure 3 shows a Williamson-Hall plot of the semiconductor materials of Example 1 (with post-annealing treatment) and Example 2 (without post-annealing treatment). As shown in the figure, the post-annealing treatment confirmed the growth of crystallites and the relaxation of non-uniform strain. 4 shows an SEM image (magnification: 10,000 times) of the semiconductor material of Example 2. As shown in the figure, it was confirmed that a powder-like semiconductor material was obtained.

[0072] C. Preparation of compacts Example 10: Fabrication of semiconductor layer 97.29 parts of zirconia balls (1 mm) were placed in a 45 mL zirconia pot (manufactured by Fritsch Japan Co., Ltd.) followed by the addition of 0.07 parts of BiOS2 from Example 2, 0.01 parts of DISPERBYK-145 (manufactured by BYK-Chemie KK), and 2.63 parts of 1-butanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.).

[0073] This mixture was dispersed using a planetary ball mill (Fritsch Japan Co., Ltd., P-5) with planetary stirring. The dispersion conditions were room temperature, 400 rpm, and 30 minutes. After dispersion, the particle size of the resulting dispersion was measured using a Zetasizer Nano ZSP (Malvern Panalytical). The Z-average particle size of the resulting dispersion was 237 nm. Furthermore, the ratio of this semiconductor material to the total solids (non-volatile components removed by distillation of solvents, etc.) before dilution (hereinafter referred to as the solids ratio) was 90.4%, and the ratio of the total solids to the total mass of the dispersion (hereinafter referred to as the concentration) was 3.4%. The dispersion was then filtered through a 0.2 μm pore size PTFE filter (Tomsic, NP-42225-ACF) to obtain a dispersion with a Z-average particle size of 120 nm. After dilution, the solid content was 81.2% and the concentration was 1.7%. The Z-average particle size was measured at 25°C, and the solution was diluted with 1-butanol as necessary.

[0074] The dispersion was spin-coated onto a cleaned glass substrate to prepare a semiconductor layer with a film thickness of 150 nm after drying. The transmittance T and reflectance R of this semiconductor layer were measured using a spectrophotometer (Hitachi High-Tech U-4000), and the absorptance was calculated as A = 100 - (T + R). To observe the particle state after dispersion, the coating film before filtering was formed by the drop-cast method and observed with an SEM. The filtered dispersion was spin-coated to form a semiconductor layer (film thickness 150 nm), and similarly observed with an SEM (magnification: 60 to 30,000 times).

[0075] (Example 11: Preparation of powder compact) The Bi2OS2 obtained in Example 2 was pulverized in an agate mortar under an argon atmosphere. Subsequently, a hydraulic press (manufactured by Masada Seisakusho, product number: MTP-10HP) was used in the atmosphere to apply a pressure of 300 MPa for 1 minute to uniaxially mold the powder into a 10 mm diameter disk. This was then annealed in a vacuum at 400°C for 10 hours to obtain a green compact. The thickness was approximately 2.5 mm. The band gap of this green compact was measured to be 0.77 eV. The density was 7.13 g / cm3. 3 It was confirmed that the density was 94% of the theoretical density.

[0076] FIG. 5 shows an SEM image of the semiconductor layer surface before filtering in Example 10. As shown in the figure, flat, fine particles were observed. The particle diameters of the particles observed by SEM observation were in the range of several tens of nanometers to 5 μm. On the other hand, in the SEM observation of the semiconductor layer surface after filtering, no semiconductor particles were observed by SEM observation. This result confirmed that coarse particles were removed by filtering. Figure 6 shows the absorption spectrum of the 150 nm thick spin-coated film of Example 10. The spin-coated film was prepared using the filtered dispersion. The absorptivity of the spin-coated film at 1400 nm was 5.6%.

[0077] For this semiconductor material and compact, optical absorption was confirmed at 1400 nm, a wavelength effective in the use range of SWIR sensors, as shown in Examples 1 to 9. It is presumed that the band gap of Bi2OS2 and Bi2O2S is controlled by the crystallite size, inhomogeneous crystal distortion, lattice constant, etc., resulting in a semiconductor material with a band gap of 0.7 to 0.95 eV. [Industrial Applicability]

[0078] The semiconductor material of the present disclosure exhibits light absorption in the near-infrared region, making it suitable as a photoelectric conversion element material suitable for light-receiving elements such as optical sensors and photodetectors. In particular, SWIR light absorption excites electrons from the valence band to the conduction band of the semiconductor material, and the semiconductor material is expected to be used as a SWIR sensor that detects these electrons. It is also expected to be used as an imaging device or image sensor. Furthermore, by forming the semiconductor material into nano-sized particles, it is expected to be used as a quantum dot or a plasmon resonance particle. Furthermore, the semiconductor material of the present disclosure can provide thin semiconductor devices and is also suitable as a thermoelectric conversion material in low-temperature ranges.

Claims

1. The energy band gap is 0.7 to 0.95 eV, Composition formula Bi ２ OS ２ and the composition formula Bi ２ O ２ A semiconductor material comprising at least one of:

2. 2. The semiconductor material according to claim 1, wherein the semiconductor material has an X-ray diffraction peak top in the range of 25.3 to 26.5° or 23.8 to 24.9° in an X-ray diffraction pattern obtained by the 2θ / θ scan method of powder X-ray diffraction measurement.

3. 3. The semiconductor material according to claim 2, wherein the half-width of the X-ray diffraction peak is 0.05 to 1.2°.

4. The composition formula Bi ２ OS ２ and the composition formula Bi ２ O ２ 2. The semiconductor material according to claim 1, wherein the crystallite sizes of S are each independently 20 to 5000 Å.

5. 2. The semiconductor material according to claim 1, synthesized by a mechanochemical reaction using a mixture containing raw materials selected from the following (i) or (ii): (i) Composition formula Bi ２ O ３ and the composition formula Bi ２ S ３ (ii) Bi, S and the composition formula Bi ２ O ３

6. Obtaining a mixture containing a raw material selected from the following (i) or (ii); and synthesizing the mixture by a mechanochemical reaction to form a semiconductor material having an energy band gap of 0.7-0.95 eV. (i) Composition formula Bi ２ O ３ and the composition formula Bi ２ S ３ (ii) Bi, S and the composition formula Bi ２ O ３

7. A molded article comprising the semiconductor material according to any one of claims 1 to 5.

8. A photoelectric conversion material comprising the semiconductor material according to any one of claims 1 to 5.

9. An optical filter comprising the semiconductor material according to any one of claims 1 to 5.

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