Platinum group metal chalcogenide thin film and semiconductor material comprising said platinum group metal chalcogenide thin film

Abstract

The present invention relates to a thin film comprising a chalcogenide of Ir and Ru that are platinum group metals. This thin film is formed on a predetermined base material and includes a platinum group metal chalcogenide, the platinum group metal chalcogenide comprising any of Ir2S3 or IrS2, RuS2, or RuSe2. The thickness of the thin film is 0.5-500 nm (inclusive). In the present invention, it has been made clear, through a simulation using first principles calculation based on an experimental method and density-functional theory (DFT), that a thin film including Ir2S3, IrS2, RuS2, or RuSe2 may realize a photoelectric effect due to irradiation by near-infrared light. The present invention is characterized by a sensitivity to light of a wavelength in the near-infrared region in particular, and is a thin film comprising a platinum group metal chalcogenide of a hitherto unknown structure.

Description

[Technical Field]

[0001] The present invention relates to a semiconductor material, particularly to a thin film made of a platinum group metal chalcogenide that is effective as a semiconductor material for constituting a light-receiving element, and more particularly to a platinum group metal chalcogenide thin film using Ir or Ru as the platinum group metal. [Background technology]

[0002] LIDAR (Light Detection and Ranging) has been attracting attention in recent years as a sensing technology for remote sensing systems in self-driving cars, drones, ships, etc., as well as for facial recognition and augmented reality (AR) technologies in smartphones, tablets, etc. LIDAR is a system that detects the distance and angle to an object by irradiating the object with laser light and detecting the reflected light with a light-receiving element. Compared to detection systems using cameras or millimeter-wave radar, LIDAR has the advantage of being able to detect the distance and angle to an object with high accuracy.

[0003] The semiconductor materials that have been considered for use as light-receiving elements in optical devices such as LIDAR include HgCdTe alloys (Hg 1-X CD X Te alloy: MCT alloy) and InGaAs alloy (In 1-X Ga X However, several problems have been identified when using HgCdTe alloys or InGaAs alloys in LIDAR light-receiving elements. For example, HgCdTe alloys have a low signal-to-noise ratio at room temperature, requiring the element to be cooled for normal use. Adding a cooling mechanism to the light-receiving element unit is not desirable for drones, smartphones, and other devices where miniaturization is essential. Adding a cooling mechanism is also undesirable for automotive equipment, which is intended to operate at room temperature. InGaAs alloys also have poor responsiveness at room temperature, and furthermore, they have problems with their high operating voltage and structural instability.

[0004] Therefore, transition metal chalcogenides (hereinafter sometimes referred to as TMC) have been attracting attention as semiconductor materials that can replace HgCdTe alloys and the like. TMCs are compounds of transition metals (metals from Groups 3 to 11) and chalcogen elements excluding oxygen. Depending on the type of central metal M, TMCs exhibit unique electrical and optical semiconductor properties, and are attracting attention as constituent materials for various semiconductor devices, such as photoelectric conversion elements in light-receiving devices and field-effect transistors (FETs).

[0005] Another advantage of TMC is its flexibility in manufacturing methods. It can be applied to a variety of thin-film formation processes without being limited to a specific method. In particular, TMCs can be manufactured using chemical vapor deposition (CVD) and atomic layer deposition (ALD), which are known for their high-yield thin-film formation processes. Furthermore, there is a wide range of substrate materials available, including silicon wafers and glass substrates (SiO2). In contrast, the use of molecular beam epitaxy (MBE) is essential for the production of HgCdTe alloys and other materials with desired compositions. Furthermore, the substrate materials are limited to expensive materials such as CdZnTe and GaAs. This flexibility in manufacturing methods and substrates allows TMCs to be produced as low-cost, high-performance semiconductor materials.

[0006] To date, specific transition metal chalcogenides known include sulfides and selenides of transition metals such as Mo, W, Hf, and Zr. In particular, many research examples have been reported on devices utilizing MoS2, a TMC of Mo.

[0007] The TMCs that the present applicant focuses on are chalcogenides that use platinum group metals (Pt, Pd, etc.) as transition metals. While there have not been many studies on platinum group metal TMCs, they have been reported to have more favorable properties than the above-mentioned Mo, W, and other TMCs. For example, for application to light-receiving elements targeting the near-infrared region used in the above-mentioned LDAR, optimizing the band gap of the semiconductor material that constitutes the light-receiving element is important. Regarding optimizing this band gap, based on the photon energy equation (E=hc / λ (h: Planck's constant, c: speed of light, λ: wavelength)), in order to achieve responsiveness in the near-infrared region, assuming a wavelength range of 700 nm to 1200 nm, the band gap of the semiconductor material must be lower than approximately 1.77 eV. In a study conducted by the present inventors prior to the present invention, it was confirmed that Pt (platinum) TMCs exhibit band gaps of 1.20 eV (single layer) to 0.21 eV (double layer) for PtSe2 and 2.66 eV (single layer) to 0.25 eV (double layer) for PtS2. These TMCs are layered compounds, and their properties can be adjusted by the number of layers, but the band gaps mentioned above are approximately 1 eV smaller than those of TMCs such as Mo. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 6-9240 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-165359 [Patent Document 3] Special Publication No. 2018-525516 Summary of the Invention [Problem to be solved by the invention]

[0009] Even if platinum group metal TMCs can exhibit favorable properties as semiconductor materials, there is still little research into platinum group metal TMCs, and not all of them can be formed into suitable materials. Furthermore, even if platinum group metal TMCs have photoresponsive and photoelectric conversion properties in the near-infrared region, if they lack stability as compounds, they are not suitable for practical use. Furthermore, as mentioned above, one of the advantages of TMCs is the high degree of freedom in terms of manufacturing methods. However, if TMCs can only be manufactured using limited manufacturing methods, their advantages are diminished.

[0010] The present invention has been made in light of the above-mentioned background, and has as its object to provide a platinum group metal chalcogenide thin film having optical semiconductor properties, particularly sensitivity to light with wavelengths in the near-infrared region, and having a hitherto unknown configuration. [Means for solving the problem]

[0011] Metals generally referred to as platinum group metals include Ag (silver), Au (gold), Pt (platinum), Pd (palladium), Ru (ruthenium), Ir (iridium), Rh (rhodium), and Os (osmium). In this regard, TMCs of Ag, Au, Pt, and Pd have been studied to some extent, and their usefulness has been confirmed. For example, sulfides and selenides (dichalcogenides: TMDCs) of Pt and Pd, such as PtS2, PtSe2, PdS2, and PdSe2, are known to have layered structures. The band gap and other properties of TMCs with layered structures can be controlled by adjusting the number of layers.

[0012] On the other hand, little is known about chalcogenides of Ru, Ir, Rh, and Os. If compounds with suitable band gaps could be found among these platinum group metal chalcogenides, they could become useful semiconductor materials. Therefore, the inventors conducted extensive research into chalcogenides of Ru, Ir, Rh, and Os based on both experimental and theoretical verification. As a result, they selected Ir and Ru from the group of platinum group metals mentioned above and discovered the usefulness of thin films of their sulfides, Ir2S3, IrS2, RuS2, and RuSe2. These TMC thin films can exhibit optical semiconductor properties and are characterized by their stability and relative ease of fabrication.

[0013] That is, the present invention provides a thin film formed on a substrate and containing a platinum group metal chalcogenide, characterized in that the platinum group metal chalcogenide is Ir2S3 or any one of IrS2, RuS2, and RuSe2, and the film thickness of the thin film is 0.5 nm or more and 500 nm or less.

[0014] As described above, in the present invention, Ir and Ru are selected as platinum group metals, and the TMC thin film is made of sulfides of these metals. The structure of the platinum group metal chalcogenide thin film according to the present invention and its manufacturing method will be described below.

[0015] (A) Structure of the Platinum Group Metal Chalcogenide Thin Film of the Present Invention (A-1) Composition of platinum group metal chalcogenide thin films As described above, the present invention is directed to a platinum group metal chalcogenide thin film using Ir or Ru as the platinum group metal. Here, the chalcogen elements constituting Ir chalcogenides include S (sulfur), Se (selenium), and Te (tellurium). The reason why Ir chalcogenides are limited to sulfides in the present invention is that they are believed to have a suitable band gap. For example, Ir selenides (IrSe2, Ir3Se8) are believed to have a too low band gap. Furthermore, Ir sulfides include Ir2S3 (diiridium trisulfide), IrS2 (diiridium disulfide), and Ir3S8 (triiridium octasulfide). From the viewpoint of band gap, the present invention is limited to a thin film composed of Ir2S3 (diiridium trisulfide) and IrS2 (diiridium disulfide).

[0016] For the same reasons as above, the present invention limits Ru chalcogenides to RuS2 (ruthenium disulfide), a Ru sulfide, and RuSe2 (ruthenium diselenide), a Ru selenide. The appropriate band gap in the present invention is a band gap that is advantageous for the photoelectric effect in the near-infrared region. The present invention assumes that the wavelength range of the near-infrared region is 700 nm or more and 2500 nm or less, and the appropriate band gap is 0.49 eV or more and 1.77 eV or more.

[0017] In addition to the above-mentioned viewpoint of optimizing the band gap, the reason for selecting Ir2S3, IrS2, RuS2, and RuSe2 as platinum group metal chalcogenides is that these sulfides are predicted to have thermal and chemical stability and are considered suitable as constituent materials for semiconductor devices.

[0018] Furthermore, unlike Pt and Pd chalcogenides, Ir and Ru chalcogenides (sulfides) have a three-dimensional crystal structure without a layered structure. In TMCs, which do not have a layered structure, characteristics such as the band gap are inherent to the material, and the band gap is unlikely to change with the number of layers (thickness). This leads to the advantage that the film thickness can be adjusted as needed depending on the design of the device to which it is applied.

[0019] The platinum group metal chalcogenide constituting the thin film of the present invention preferably has a high purity, preferably 99% or higher, and more preferably 99.9% or higher. In this case, the purity is determined by either the total mass of Ir and S or the total mass of Ru and S, based on the mass of the entire thin film. In addition, the present invention allows the inclusion of unavoidable impurities. Examples of unavoidable impurities contained in the thin film include platinum group elements other than Ir and Ru, and Group 4 elements (e.g., Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, etc.). The total amount of these unavoidable impurities is preferably 100 ppm or less.

[0020] (A-2) Structure of platinum group metal chalcogenide thin films The platinum group metal chalcogenide thin film of the present invention is 0.5 nm or more and 500 nm or less. If it is less than 0.5 nm, it is difficult to form the crystal structure of the platinum group metal chalcogenide, and the desired characteristics may not be obtained. Furthermore, although it is possible to manufacture a TMC thin film with a thickness exceeding 500 nm, this should be limited because it requires more materials and is less cost-effective. The thickness of the TMC thin film is preferably 0.5 nm or more and 200 nm or less.

[0021] The thin film may be formed over the entire substrate surface, or it may be formed as an island-like thin film partially covering the substrate. This is because the interaction between the scattered TMC crystals in an island-like pattern can exhibit semiconducting properties even if the TMC crystals are not a continuous film over the entire surface. An island-like thin film is a thin film formed using a growth morphology based on the Volmer-Weber type. This is a state in which three-dimensional islands of platinum group metal chalcogenide are formed on the substrate. This refers to the transitional state until the platinum group metal chalcogenide thin film is completely formed on the substrate. Including the case of the island-like thin film, the coverage of the platinum group metal chalcogenide thin film on the substrate is preferably 10% or greater. The coverage is calculated as the ratio of the surface area of ​​the platinum group metal chalcogenide thin film to the surface area of ​​the substrate on which the thin film is formed.

[0022] The platinum group chalcogenide thin film (including island-shaped thin films) of the present invention may contain at least one of Ir2S3, IrS2, RuS2, and RuSe2 on the surface. In other words, the interior of the thin film may contain metallic Ir or metallic Ru, or compounds that have not been chalcogenized (sulfurized or selenized) to Ir2S3, IrS2, RuS2, or RuSe2. As will be described in detail later, a metal film reaction method for chalcogenizing a metal film (Ir film, Ru film) can be used to manufacture the TMC thin film of the present invention. In this manufacturing method, chalcogenization of the metal film proceeds from the surface, so the desired platinum group metal chalcogenide is formed on the thin film surface, but the interior of the thin film may not be sufficiently chalcogenized. Furthermore, multi-target sputtering can also be used to manufacture the TMC thin film, but differences in sputtering efficiency can result in the presence of metal portions within the thin film. In the present invention, thin films in this state are acceptable. When the TMC thin film of the present invention is used as a light-receiving element or the like, it is sufficient that Ir2S3, IrS2, RuS2, and RuSe2 are present on the surface that comes into contact with an external electrode. Of course, the entire thin film, including the interior, may be composed of Ir2S3, IrS2, RuS2, and RuSe2.

[0023] (A-3) Base material The thin film of platinum group metal chalcogenide according to the present invention is formed on an appropriate substrate. The substrate is a member for supporting the thin film. Any material may be used for the substrate as long as it can support the platinum group metal chalcogenide thin film. Examples of the material include glass, quartz, silicon, ceramics, and metal. The shape and dimensions of the substrate are not particularly limited.

[0024] (B) Semiconductor material comprising a platinum group metal chalcogenide thin film according to the present invention The platinum group metal chalcogenide thin film according to the present invention is useful as a semiconductor material for photoelectric conversion and light absorption / emission. This semiconductor material can be used, for example, as a photoelectric conversion element for optical devices such as light-receiving devices, optical sensors, and photodetectors. The semiconductor material according to the present invention also has good sensitivity to light with wavelengths in the near-infrared region. Therefore, it is particularly suitable as a light-receiving element for LIDAR and SWIR image sensors.

[0025] (C) Method for producing a platinum group metal chalcogenide thin film according to the present invention Next, a method for manufacturing a platinum group metal chalcogenide thin film according to the present invention will be described. The platinum group metal chalcogenide thin film according to the present invention is manufactured by forming a film of platinum group metal chalcogenide on the above-mentioned substrate. The film formation method is not particularly limited, and conventional methods for manufacturing transition metal chalcogenides can be applied. As a method for manufacturing a platinum group metal chalcogenide according to the present invention, a metal film reaction method can be used, in which a thin film of a platinum group metal (Ir, Ru) is formed on a substrate and then heat-treated in a chalcogen atmosphere (sulfur atmosphere or selenium atmosphere) to chalcogenize (sulfurize or selenize) the platinum group metal film.

[0026] As a method for forming a platinum group metal thin film (Ir thin film, Ru thin film), known thin film formation processes such as physical vapor deposition methods such as sputtering and vacuum evaporation, and chemical vapor deposition methods such as chemical vapor deposition (CVD) and atomic layer deposition (ALD) can be applied. In particular, sputtering and chemical vapor deposition can efficiently obtain a platinum group metal thin film of a desired thickness.

[0027] When forming a platinum group metal thin film by sputtering, it is preferable to use an Ir target or Ru target. Normal sputtering conditions can be used. It is preferable to use high-purity Ir and Ru targets with a metal content of 99% or more.

[0028] The basic steps in the chemical vapor deposition (CVD and ALD) film formation process involve vaporizing a metal compound that serves as a precursor for the thin film, supplying the resulting precursor gas to a substrate, and causing a chemical reaction (decomposition or synthesis) in the gas phase to deposit the target substance on the substrate to form a film. Examples of platinum group metal precursors that can be used in chemical vapor deposition include organic iridium compounds such as tricarbonyl[(1,2,3-η)-1,2,3-tris(1,1-dimethylethyl)-2-cyclopropen-1-yl]iridium (TICP), tris(acetylacetonato)iridium (Ir(acac)3), and (cyclohexadienyl)methylcyclopentadienyliridium ((MeCp)Ir(CHD)). For Ru, organic ruthenium compounds such as tricarbonyl(trimethylenemethane)ruthenium ([Ru(TMM)(CO)3), dicarbonyl-bis(5-methyl-2,4-hexanedionato)ruthenium, hexacarbonyl[methyl-(1-methylpropyl)-butene-aminato]diruthenium, and dodecacarbonyltriruthenium (DCR) can be used.

[0029] In addition, in chemical vapor deposition, a reactive gas is generally supplied to the substrate surface to promote decomposition of the metal compound in the source gas. The reactive gas may be oxygen, hydrogen, or the like depending on the type of precursor (metal compound), and is not particularly limited in the present invention. Other film formation conditions in CVD and ALD are the same as those in ordinary chemical vapor deposition.

[0030] A platinum group metal (Ir, Ru) thin film is formed to a thickness corresponding to the desired thickness of the platinum group metal chalcogenide. The formed platinum group metal thin film is then treated in a chalcogen atmosphere to produce the platinum group metal chalcogenide thin film. Hydrogen sulfide (HS) gas or selenium hydride (HSe) can be used to form the chalcogen atmosphere. Solid sulfur or selenium can also be used, and can be vaporized by heating and sublimation to form the chalcogen atmosphere. Chalcogenization of a platinum group metal thin film is preferably performed by heating the thin film in a chalcogen atmosphere. The heating temperature is preferably 800°C to 1100°C for chalcogenization of Ir, and 600°C to 1300°C for chalcogenization of Ru. At temperatures below the lower limit of the above temperature range, chalcogenization may be insufficient, while temperatures above the upper limit may result in decomposition of the chalcogenide. Regarding the chalcogenization of Ir, the formation of Ir2S3 can be preferentially caused by treating at a high temperature within the above temperature range. The heating time is preferably 30 minutes to 12 hours.

[0031] In addition to the metal film reaction methods described above, platinum group metal chalcogenide thin films can also be produced by directly forming a platinum group metal chalcogenide on a substrate. For example, in sputtering, a platinum group metal chalcogenide thin film can be produced by reactive sputtering using a platinum group metal target. Alternatively, a platinum group metal chalcogenide thin film can be produced by producing a platinum group metal chalcogenide by powder metallurgy or other methods and using this as a sputtering target. When using chemical vapor deposition, a platinum group metal chalcogenide thin film can be synthesized directly on a substrate by using a chalcogen source (e.g., H2S gas or Se vapor) as a reactive gas. Alternatively, a platinum group metal chalcogenide thin film can be produced by transferring or applying a platinum group metal chalcogenide synthesized in a separate container or on a substrate to the substrate. [Effects of the Invention]

[0032] As described above, the present invention relates to a platinum group metal chalcogenide thin film that uses Ir and Ru as the platinum group metal. The platinum group metal chalcogenide thin film of the present invention has an appropriate band gap for use as a semiconductor material for constituting a light-receiving element or the like. In particular, it has sensitivity to light with wavelengths in the near-infrared region, and is expected to respond to devices incorporating light-receiving elements in this region. Furthermore, the platinum group metal chalcogenide thin film of the present invention has a high degree of freedom in its manufacturing method, can be manufactured by various thin film manufacturing methods, and is also stable. [Brief explanation of the drawings]

[0033] [Figure 1] 1A and 1B are diagrams showing the results of XPS analysis of the Ir2S3 thin film and the RuS2 thin film produced in the first embodiment. [Figure 2] 10A and 10B are graphs showing the evaluation results of the photoresponse characteristics (740 nm, 850 nm, 940 nm) of the Ir2S3 thin film and the RuS2 thin film manufactured in the first embodiment. [Figure 3] 10A and 10B are diagrams showing the results of XPS analysis of the Ir2S3 thin film and the RuS2 thin film produced in the second embodiment. [Figure 4] 10A and 10B are graphs showing the evaluation results of the photoresponse characteristics (740 nm, 850 nm, 940 nm) of the Ir2S3 thin film and the RuS2 thin film manufactured in the second embodiment. [Figure 5] 10A and 10B are diagrams showing the results of XRD analysis of the RuS2 thin films produced in the first and second embodiments. [Figure 6] Figure showing the electron density of states in Ir2S3 and RuS2 obtained by DFT calculation. [Figure 7] Photoresponse characteristics of RuSe2 thin film manufactured in the fourth embodiment DETAILED DESCRIPTION OF THE INVENTION

[0034] First embodimentHereinafter, an embodiment of the present invention will be described. In this embodiment, an Ir thin film and a Ru thin film were formed by sputtering, and then chalcogenized to produce a platinum group metal chalcogenide thin film. The photoresponse characteristics of these platinum group metal chalcogenide thin films to near-infrared light were evaluated.

[0035] [Fabrication of platinum group metal chalcogenide thin films] The deposition of the Ir and Ru thin films was performed using a magnetron sputtering system with 99.99% purity Ir and Ru targets. The substrate was a Si / SiO2 substrate (surface oxidized to 280 nm, dimensions: 20 x 20, thickness 1.5 mm). The deposition conditions were as follows: cleaning was performed by pre-sputtering at 50 W for 10 seconds, followed by sputtering at 50 W. The chamber pressure during deposition was 0.7 Pa. Then, Ir and Ru thin films with thicknesses of 1.0 nm and 2.0 nm were deposited.

[0036] The chalcogenization of the thin films was carried out by placing the substrate on which the film was formed in a tubular furnace, introducing H2S into the furnace, and heating it under an air flow of 10 sccm. The heating temperature was 900°C for the Ir film and 800°C for the Ru film, and both were heat-treated for 1 hour.

[0037] The manufactured platinum group metal chalcogenide thin films were analyzed by X-ray photoelectron spectroscopy (XPS). The results of this XPS analysis are shown in Figure 1. For the RuS2 thin film, the difference in peak position (binding energy) between the Ru3p spectrum of metallic Ru and RuS2 is narrow, approximately 0.2 eV, so the S2p spectrum measurement results are also shown. The results of the XPS analysis confirmed that a thin film containing Ir2S3 and a thin film containing RuS2 were formed in this embodiment. Regarding the Ir2S3 thin film, although metallic Ir partially remained, it can be said that Ir2S3 was present on the surface. Furthermore, AFM measurements were performed to measure the actual film thickness of the platinum group metal chalcogenide thin film. The results for the Ir2S3 thin film were 1.8 nm (1 nm before heat treatment) and 2.5 nm (2 nm before heat treatment). The thicknesses for the RuS2 thin film were 1.5 nm (1 nm before heat treatment) and 2.3 nm (2 nm before heat treatment).

[0038] [Evaluation of light response] The photoresponse characteristics of the platinum group metal chalcogenide thin films (Ir2S3 thin film, RuS2 thin film) fabricated above were evaluated as semiconductor characteristics. In this embodiment, a comb-shaped electrode was formed on the surface of the fabricated thin film to fabricate a photodetector, which is a photoelectric conversion element. The comb-shaped electrode was formed by patterning a Ti film (5 nm thick) and an Au film (40 nm thick) in this order into a comb shape on the surface of the platinum group metal chalcogenide thin film.

[0039] The photoresponse of the fabricated photodetectors to near-infrared light was then measured. The measurement method involved irradiating each photodetector with near-infrared light and measuring the photocurrent at room temperature using a multimeter. The wavelengths of the irradiated near-infrared light were set to three patterns: 740 nm, 850 nm, and 940 nm, and the response characteristics were measured at each wavelength. The near-infrared light was irradiated intermittently for 20 seconds with a 30-second interval. A bias voltage of 3.0 V was applied from the multimeter.

[0040] The evaluation results of the photoresponse characteristics of the platinum group chalcogenide thin film of this embodiment are shown in Figure 2. From these measurement results, it was confirmed that the platinum group metal chalcogenide thin films (Ir2S3 thin film (1.0 nm, 2.0 nm), RuS2 thin film (1.0 nm, 2.0 nm)) manufactured in this embodiment exhibit photoresponse in the near-infrared region of 740 nm to 940 nm.

[0041] Second embodiment In this embodiment, a Ru thin film and an Ir thin film were formed by chemical vapor deposition, and the metal thin films were chalcogenized to produce a platinum group metal chalcogenide thin film.Then, the photoresponse characteristics were evaluated in the same manner as in the first embodiment.

[0042] [Fabrication of platinum group metal chalcogenide thin films] The same substrate (Si / SiO2 substrate) as in the first embodiment was prepared, and Ru and Ir thin films were formed on this substrate by the ALD method. The ALD method is a thin film formation process that repeats a cycle consisting of the following steps: an adsorption step in which raw material gas is introduced into a reactor and the raw material is adsorbed onto the substrate surface; a purging step in which excess raw material gas is exhausted; a reaction step in which a reactive gas is introduced into the reactor and the raw material adsorbed on the substrate surface is reacted with the reactive gas to precipitate metal; and a purging step in which excess reactive gas is exhausted. First, the substrate was placed in an ALD apparatus, and the reactor was purged with nitrogen gas (100 sccm) before film formation.

[0043] The Ru thin film was formed using a Ru complex, tricarbonyl(trimethylenemethane)ruthenium ([Ru(TMM)(CO)3), as a precursor. The Ru thin film was formed under the following film formation conditions. The film thickness was controlled by adjusting the number of cycles (1) to (4). In this embodiment, three types of samples were fabricated using ALD with 42 cycles (film thickness: 4 nm) and 50 cycles (film thickness: 6 nm). (1) Adsorption process ·Raw material heating temperature: 10℃ Carrier gas: Nitrogen / 50sccm Introduction time: 10 seconds (2) Raw material gas purge process Purge with nitrogen gas (100sccm) Introduction time: 10 seconds (3) Reaction step Reactive gas: pure oxygen / 50sccm Introduction time: 10 seconds (4) Reaction gas purge process Purge with nitrogen gas (100sccm) Introduction time: 10 seconds

[0044] The Ir thin film was produced using the Ir complex tricarbonyl[(1,2,3-η)-1,2,3-tris(1,1-dimethylethyl)-2-cyclopropen-1-yl]iridium as a precursor. The Ir2S3 thin film was formed under the following film formation conditions. The number of cycles was 384 cycles (film thickness: 4 nm) and 412 cycles (film thickness: 4 nm).

[0045] (1) Adsorption process ·Raw material heating temperature: 55℃ Carrier gas: Nitrogen / 100sccm Introduction time: 7 seconds (2) Raw material gas purge process Purge with nitrogen gas (100sccm) Introduction time: 10 seconds (3) Reaction step Reactive gas: pure oxygen / 50sccm Introduction time: 2 seconds (4) Reaction gas purge process Purge with nitrogen gas (100sccm) Introduction time: 10 seconds

[0046] The formed Ru thin film and Ir thin film were then chalcogenized under the same conditions as in the first embodiment to form platinum group metal chalcogenide thin films. Figure 3 shows the results of XPS analysis. It was confirmed that Ir2S3 and RuS2 were formed in this embodiment. Furthermore, AFM measurements were performed to measure the thickness of the platinum group metal chalcogenide thin films. The Ir2S3 thin film had a thickness of 4.9 nm (4 nm before heat treatment) and 6.5 nm (6 nm before heat treatment), while the RuS2 thin film had a thickness of 4.4 nm (4 nm before heat treatment) and 8.8 nm (6 nm before heat treatment).

[0047] [Evaluation of light response] Using the manufactured platinum group metal chalcogenide thin films (Ir2S3 thin film and RuS2 thin film), photodetectors were manufactured in the same manner as in the first embodiment. Then, the photoresponse characteristics of these photodetectors in the near-infrared region were evaluated. The measurement method was the same as in the first embodiment, and the wavelength of the irradiated near-infrared light was set to three patterns: 740 nm, 850 nm, and 940 nm, and the response characteristics at each wavelength were measured.

[0048] The evaluation results of the photoresponse characteristics of the Ir2S3 thin film and RuS2 thin film of this embodiment are shown in Figure 4. It was confirmed that the platinum group metal chalcogenide thin film of this embodiment also exhibits photoresponse in the near-infrared region of 740 nm to 940 nm. Note that the platinum group metal chalcogenide thin films of the first embodiment and this embodiment are both manufactured by a metal film reaction method in which a metal thin film is sulfurized. It can be said that the difference in the manufacturing method of the metal film (sputtering method, ALD method) does not affect the presence or absence of photoresponse.

[0049] However, when comparing the first embodiment (sputtering method) with the present embodiment (ALD method), the platinum group metal chalcogenide thin film of the present embodiment has a higher photocurrent value, despite the difference in film thickness. This difference is presumably due to the crystallinity of the platinum group metal chalcogenide. To clarify this point, Figure 5 shows the results of XRD analysis of the RuS2 thin films produced in the first embodiment and the present embodiment. Figure 5 shows that the thin film produced in the present embodiment is composed of highly crystalline RuS2. On the other hand, in the thin film produced in the first embodiment, the RuS2 peak is difficult to distinguish, and a metallic Ru peak is also observed. The XPS analysis results for the first embodiment (Figure 2) confirm the formation of RuS2, but it is thought that the metallic Ru inside the thin film, which cannot be detected by XPS, was confirmed by XRD. From this, it is considered that while it is sufficient to form RuS2 (Ir2S3) at least on the surface to impart optical semiconductor properties to the thin film, sulfurization throughout the thin film is preferable for generating a stronger photocurrent.

[0050] Third embodimentThis embodiment explains the results of an investigation into the properties of platinum group metal chalcogenides through theoretical verification in addition to the experimental verifications of the first and second embodiments. In this investigation, simulations were performed using first-principles calculations based on density functional theory (DFT). DFT is a theory that states that physical properties such as the electron distribution and energy of the ground state of an interacting multi-electron system can be calculated using electron density functions. DFT-based first-principles calculations are a calculation method based on the density functional theory. First-principles calculations enable quantitative investigation of the electronic structure of a material without experimental or empirical parameters.

[0051] In this embodiment, the electronic state was simulated using VASP, a first-principles calculation application (DFT code) based on density functional theory. The atomic structure data in the Materials Project, a general-purpose database, was used for the simulation (see A. Jain et al., "The Materials Project: A Materials genome approach to accelerating materials innovation”,APL Materials, 2013, 1(1), 011002). In this embodiment, the band gaps (bulk state) of chalcogenides (sulfides, selenides) of the platinum group metals Ir, Ru, and Rh were calculated.

[0052] DFT calculations can provide DOS information (electron density of states information) for various platinum group metal chalcogenides. As an example, Figure 6 shows the DOS calculation results for Ir2S3 and RuS2. Based on the obtained DOS information, the band gaps of various platinum group metal chalcogenides were calculated. The band gaps and absorption wavelengths of various chalcogenides of Ir, Ru, and Rh are shown in Tables 1 to 3.

[0053] [Table 1]

[0054] [Table 2]

[0055] [Table 3]

[0056] From the DFT calculation results in Tables 1 to 3, it was first confirmed that Rh has a low band gap and therefore does not easily exhibit the properties required for the semiconductor material of the present invention.

[0057] Furthermore, it can be seen that Ir and Ru show results different from those of Rh and can exhibit suitable band gaps. With Ru, selenide (RuSe2) tends to have a low band gap, and sulfide (RuS2) is suitable. However, it must be taken into consideration that these band gap values ​​are calculated using semi-DFT and are therefore underestimated compared to the actual band gap. In other words, it is considered that the practical use of RuSe2 in the near-infrared region above 1200 nm should not be excluded. This point will be confirmed in the fourth embodiment.

[0058] Similarly, sulfides of Ir show suitable values, but Ir2S3 and IrS2 in particular can show suitable band gaps. The results of the theoretical verification by DFT calculations as described above are consistent with the fact that the Ir2S3 thin film and the RuS2 thin film showed suitable photoresponse characteristics in the first and second embodiments.

[0059] Here, to confirm the above DFT calculation results, a chalcogenide thin film (RhS) using Rh as the platinum group metal was manufactured. In manufacturing the Rh chalcogenide thin film, first, an Rh thin film was formed by sputtering. The Rh thin film was formed using an Rh target with a purity of 99.99% using the same sputtering apparatus (magnetron sputtering apparatus) and under the same film formation conditions as in the first embodiment (film thickness: 2 nm). Then, similar to the first embodiment, the Rh thin film was sulfurized by heating at 900°C for 1 hour under an HS flow (10 sccm).

[0060] Next, to confirm whether the manufactured Rh2S3 thin film was conductive, the IV curve was measured using the four-terminal method. A tendency for the voltage to increase with increasing current was observed. In other words, this Rh2S3 thin film is a conductor. From Table 3 above, the band gap of Rh2S3 calculated by DFT is extremely small at 0.192 eV, which is inferred to be a conductor, and this agrees with the measurement results.

[0061] Fourth embodiment In this embodiment, a RuSe2 thin film, which was suggested to have a small band gap by the above-mentioned DFT calculation, was fabricated, and its photoresponse at 1550 nm was confirmed. In this embodiment, a Ru thin film was formed by chemical vapor deposition, and the metal thin film was selenized to produce a RuSe2 thin film. The photoresponse characteristics were then evaluated in the same manner as in the first and second embodiments.

[0062] [Fabrication of RuSe2 thin film] The same substrate (Si / SiO2 substrate) as in the first and second embodiments was prepared, and a Ru thin film was formed on this substrate by the ALD method. The ALD method is a thin film formation process that repeats a cycle consisting of the following steps: an adsorption step in which raw material gas is introduced into a reactor and the raw material is adsorbed onto the substrate surface; a purging step in which excess raw material gas is exhausted; a reaction step in which a reactive gas is introduced into the reactor and the raw material adsorbed on the substrate surface is reacted with the reactive gas to precipitate metal; and a purging step in which excess reactive gas is exhausted. First, the substrate was placed in an ALD apparatus, and the reactor was purged with nitrogen gas (100 sccm) before film formation.

[0063] The Ru thin film was formed using a Ru complex, tricarbonyl(trimethylenemethane)ruthenium ([Ru(TMM)(CO)3), as a precursor. The Ru thin film was formed under the following film formation conditions. The film thickness was controlled by adjusting the number of cycles (1) to (4). In this embodiment, a sample was fabricated after 42 cycles (film thickness: 4 nm). (1) Adsorption process ·Raw material heating temperature: 10℃ Carrier gas: Nitrogen / 50sccm Introduction time: 10 seconds (2) Raw material gas purge process Purge with nitrogen gas (100sccm) Introduction time: 10 seconds (3) Reaction step Reactive gas: pure oxygen / 50sccm Introduction time: 10 seconds (4) Reaction gas purge process Purge with nitrogen gas (100sccm) Introduction time: 10 seconds

[0064] To selenize the thin film, the substrate and selenium powder were placed in a tubular furnace and heated under a 10 sccm argon gas flow. The selenium powder was placed upstream of the gas flow in the furnace so that the argon gas would transport the selenium vapor. The heating temperature was 800°C for the substrate and 220°C for the selenium powder, and the heat treatment was carried out for one hour. After selenization, the film thickness became 12 nm.

[0065] [Evaluation of light response] Using the produced RuSe2, photodetectors were produced in the same manner as in the first and second embodiments. The photoresponse characteristics of these photodetectors in the near-infrared region were evaluated. The measurement method was the same as in the first embodiment, and the wavelength of the irradiated near-infrared light was 1550 nm, and the response characteristics were measured.

[0066] The evaluation results of the photoresponse characteristics of the RuSe2 thin film of this embodiment are shown in Figure 7. It was confirmed that the RuSe2 thin film of this embodiment can exhibit photoresponse in the near-infrared region of 1550 nm. [Industrial Applicability]

[0067] As described above, the present invention demonstrates that Ir2S3 thin films, IrS2 thin films, RuS2 thin films, and RuSe2 thin films are useful as new platinum group metal chalcogenide thin films. The platinum group metal chalcogenide thin films of the present invention have an appropriate band gap as semiconductor materials for constituting light-receiving elements and the like, and are also sensitive to light with wavelengths in the near-infrared region. The platinum group metal chalcogenide thin films of the present invention are relatively easy to manufacture and offer a high degree of flexibility. Furthermore, these platinum group metal chalcogenide thin films also have good stability. As a new semiconductor material, the present invention has potential for use in light-receiving elements of optical devices such as LIDAR and SWIR image sensors.

Claims

1. A thin film formed on a substrate and including a platinum group metal chalcogenide, the platinum group metal chalcogenide is made of Ir 2 S 3 , RuS 2 , or RuSe 2; the thin film is composed of a three-dimensional crystal structure in which crystals of the platinum group metal chalcogenide are continuous, The film thickness of the thin film is 4.4 nm or more and 500 nm or less.

2. 2. The thin film according to claim 1, wherein the thickness of the thin film is 4.4 nm or more and 200 nm or less.

3. 2. The thin film according to claim 1, which is formed in an island shape on a substrate.

4. A semiconductor material comprising a substrate and the thin film according to any one of claims 1 to 3 formed thereon.

5. A light-receiving element comprising the semiconductor material according to claim 4.

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