Semiconductor material having a transition metal dichalcogenide thin film, its manufacturing method, and light-receiving element having the semiconductor material

Abstract

The present invention relates to a semiconductor material in which a thin film comprising a transition metal dichalcogenide given by MX2 (M is a transition metal and X is a chalcogen atom other than oxygen) is formed on a base material. The semiconductor characteristics of the thin film are improved in the present invention by modifying the defect sites of the transition metal dichalcogenide thin film surface by modifying metal nanoparticles comprising a metal N on the thin film. The metal nanoparticles are preferably noble metal nanoparticles. In addition, a sulfide, selenide, or telluride of Pt or Pd is preferred for the transition metal M of the transition metal dichalcogenide thin film on the base material. The application of atomic layer deposition (ALD) is particularly preferred for the modification process for the metal nanoparticles.

Description

[Technical Field]

[0001] The present invention relates to a semiconductor material having a thin film made of a transition metal dichalgogenide, and more particularly to a semiconductor material having a transition metal dichalgogenide thin film in which surface defects have been repaired and which has excellent response characteristics, and a method for producing the same. [Background technology]

[0002] In recent years, transition metal dichalcogenides (TMDCs) have been attracting attention as semiconductor materials for use in light-receiving devices such as photodetectors and solar cells, as well as semiconductor devices such as field-effect transistors (FETs). Transition metal dichalcogenides are compounds (MX2) of a metal (M) belonging to Groups 3 to 11 of the transition metals, and a chalcogen element (X) excluding oxygen. Depending on the type of central metal M, transition metal dichalcogenides exhibit unique electrical and optical semiconductor properties, which allows them to be used in the various applications mentioned above (for example, Patent Document 1).

[0003] One application where transition metal dichalcogenides are particularly promising is as photoelectric conversion elements that constitute light-receiving elements in sensors and other devices. One example is a light-receiving element used in LIDAR (Light Detection and Ranging). LIDAR is a sensing technology that uses laser light. It irradiates an object with laser light and detects the reflected light with a light-receiving element to detect the distance and angle to the object. Compared to detection systems using cameras or millimeter-wave radar, LIDAR has the advantage of being able to detect the distance and angle to the object with high accuracy. LIDAR has been used as a remote sensing technology in autonomous driving automobiles, drones, ships, and other applications. Recently, LIDAR has also been applied to facial recognition and augmented reality (AR) technologies on smartphones and tablets.

[0004] To date, the semiconductor materials that have been considered for use in LIDAR light-receiving elements include HgCdTe alloy (Hg1-X CD X Te alloy: MCT alloy) and InGaAs alloy (In 1-X Ga X As alloys) can be cited (for example, Patent Document 2 and Patent Document 3). The band gap of these semiconductor alloys can be adjusted by setting an appropriate composition (x), and they are capable of detecting infrared rays over a wide range of 1 to 30 μm. Light-receiving elements (photoconductive elements) using these alloys are already commercially available.

[0005] However, several issues have been raised when using HgCdTe and InGaAs alloys in LIDAR light-receiving elements. These issues primarily stem from performance issues. HgCdTe alloys have a low signal-to-noise ratio at room temperature, requiring cooling of the elements to operate without noise. The cooling temperature is said to be below 80 K. Therefore, systems operated at room temperature require the addition of a cooling mechanism, which is undesirable for drones, smartphones, and other devices where miniaturization is essential. Furthermore, they are difficult to use in automotive equipment, which must operate at room temperature. Furthermore, InGaAs alloys have also been noted to have poor responsiveness at room temperature, and in addition, they suffer from high operating voltages and structural instability.

[0006] Additionally, devices using HgCdTe alloys and InGaAs alloys pose cost issues. To produce these alloys with the desired composition, molecular beam epitaxy (MBE) is essential. MBE is a thin-film formation process performed under ultra-high vacuum, and the time required to form a thin film of the desired thickness is long, resulting in low manufacturing efficiency. Furthermore, when producing HgCdTe and InGaAs alloys using MBE, the substrate material is limited to expensive materials such as CdZnTe and GaAs. Due to these manufacturing efficiency and substrate costs, photodetectors using HgCdTe and InGaAs alloys are expensive. This cost issue is a barrier to the widespread use of LIDAR.

[0007] Therefore, transition metal dichalcogenides are expected to be used as light-receiving elements for LIDAR and other applications. Transition metal dichalcogenides are two-dimensional materials with a layered structure, and can exhibit photoresponsiveness with a band gap that changes depending on the number of layers. Furthermore, transition metal dichalcogenides have been reported to have a high signal-to-noise ratio at room temperature, which could solve the performance problems associated with use at room temperature.

[0008] Transition metal dichalcogenides can also be manufactured using a variety of thin film formation processes. In particular, they can be manufactured using chemical vapor deposition methods such as chemical vapor deposition (CVD) and atomic layer deposition (ALD). Chemical vapor deposition is known as a high-yield thin film formation process. Furthermore, when manufacturing transition metal dichalcogenides using chemical vapor deposition, there is a wide range of substrate materials to choose from, and films can be formed on Si wafers and glass substrates (SiO2). Therefore, semiconductor materials made from transition metal dichalcogenides are considered to have an advantage in terms of cost as well. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Special Publication No. 2018-525516 [Patent Document 2] Special Publication No. 6-9240 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-165359 Summary of the Invention [Problem to be solved by the invention]

[0010] As mentioned above, transition metal dichalcogenides offer many advantages over conventional optical semiconductor materials such as HgCdTe alloys. However, transition metal dichalcogenides are relatively new materials, and many unknowns remain regarding their characteristic improvements and the development of efficient manufacturing processes. For application to light-receiving elements such as LIDAR, as exemplified above, not only is light sensitivity in a specified wavelength range required, but performance improvements, such as higher light sensitivity and response characteristics, are also required.

[0011] The present invention has been made in light of the above-mentioned background, and aims to provide a semiconductor material comprising a transition metal dichalcogenide thin film that can achieve improved performance compared to conventional semiconductor materials. It also presents methods for manufacturing and improving such semiconductor materials comprising a transition metal dichalcogenide thin film. [Means for solving the problem]

[0012] To address the above-mentioned issues, the present inventors conducted extensive research and focused on the presence of surface defects as a starting point for improving the performance of transition metal dichalcogenides. Transition metal dichalcogenides are two-dimensional materials in which metal atoms and chalcogen atoms are regularly arranged, bonded by ionic and / or covalent bonds. In an ideal transition metal dichalcogenide, the regular arrangement of the constituent atoms is not disrupted. However, in reality, defects exist on the surface of transition metal dichalcogenide thin films regardless of their manufacturing process. These surface defects include dislocations, lattice defects, and other factors that disrupt the regularity of the atomic arrangement, such as dangling bonds (unbonded bonds) and edge sites near lattice defects. Furthermore, these surface defects trap carriers and serve as the starting point for leakage paths due to recombination, which can prevent transition metal dichalcogenides from achieving the semiconductor properties they are designed to exhibit.

[0013] Therefore, in order to improve the performance of semiconductor materials made of transition metal dichalcogenides, it is necessary to suppress the generation of surface defects during their manufacturing process. However, it is not necessarily easy to manufacture transition metal dichalcogenides that maintain perfect order and contain no defects, and an approach based solely on the manufacturing method is hardly a realistic solution. Therefore, the present inventors have conceived the idea of ​​preferentially modifying the defect portions of the surface of a thin film of a transition metal dichalcogenide manufactured arbitrarily with metal nanoparticles to suppress carrier trapping due to the defects.

[0014] That is, the present invention provides a semiconductor material comprising a substrate and a thin film formed on the substrate and made of a transition metal dichalcogenide represented by MX2 (M is a transition metal, X is a chalcogen), the semiconductor material being characterized by comprising metal nanoparticles made of metal N and modifying the surface of the thin film.

[0015] As described above, the semiconductor material comprising a transition metal dichalcogenide according to the present invention basically comprises a substrate, a thin film made of a transition metal dichalcogenide, and metal nanoparticles on the thin film. The configuration and manufacturing method of the semiconductor material according to the present invention, as well as a light-receiving element using the semiconductor material according to the present invention, will be described below.

[0016] (A) Structure of the semiconductor material according to the present invention (A-1) Base material The substrate is a member for supporting a thin film made of a transition metal dichalgogenide. The substrate may be made of any material that can support a thin film made of a transition metal dichalgogenide. Examples of the material include glass, quartz, silicon, ceramics, and metal. The shape and dimensions of the substrate are not particularly limited.

[0017] (A-2) Transition metal dichalcogenide thin films As described above, a transition metal dichalcogenide is a compound (MX2) of a metal (M) belonging to Groups 4 to 11 of the transition metals and a chalcogen element (X) excluding oxygen. Specific examples of transition metals in the semiconductor material of the present invention include tungsten (W), molybdenum (Mo), platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), osnium (Os), iridium (Ir), hafnium (Hf), and zirconium (Zr). Examples of chalcogen elements include sulfur (S), selenium (Se), and tellurium (Te).

[0018] The preferred transition metal dichalcogenides in the present invention are those in which the transition metal is a platinum group metal (Pt, Pd). Specifically, they are PtSe2, PtS2, PtTe2, PdSe2, PdS2, and PdTe2. These transition metal dichalcogenides have a band gap that is approximately 1 eV smaller than that of transition metal dichalcogenides with Mo or W as the central metal, and have high mobility (carrier mobility), which is a characteristic of transition metal dichalcogenides, and are therefore expected to have excellent photoresponse characteristics.

[0019] Transition metal dichalcogenides are two-dimensional materials in which the constituent elements are strongly bonded by ionic and / or covalent bonds. A transition metal dichalcogenide thin film has a structure in which unit layers made of the two-dimensional material are stacked in layers. The unit layers are bonded by relatively weak bonds (van der Waals forces). The transition metal dichalcogenide thin film of the present invention can also be composed of a single unit layer or multiple unit layers. The number of layers affects the band gap of the semiconductor thin film, so the number of layers can be adjusted depending on the device to which it is applied. Therefore, there is no need to limit the thickness of the transition metal dichalcogenide thin film in the present invention. For example, for application to optical elements for LIDAR, the number of layers is preferably 1 to 4, and more preferably 1 to 2. The thickness of the thin film in this case is 0.5 to 5 nm.

[0020] (A-3) Metal nanoparticles (A-3-1) Function and composition of metal nanoparticles The surface modification of a transition metal dichalcogenide thin film with metal nanoparticles is a key feature of the present invention. In this context, "modification" refers to a state in which the metal nanoparticles are bonded to the transition metal dichalcogenide thin film through adsorption forces such as physical adsorption and chemical adsorption, or bonding forces such as metallic bonds, ionic bonds, and covalent bonds. By modifying defect sites in the transition metal dichalcogenide thin film with metal nanoparticles, carrier trapping by the defects described above is prevented. This suppresses degradation of response characteristics due to recombination of unwanted carriers.

[0021] Metal nanoparticles are nano-sized particles made of metal N. The mechanism by which metal nanoparticles prevent carrier trapping is based on the Schottky junction formed between the transition metal dichalcogenide and the metal nanoparticles. The formation of the Schottky junction causes band bending, allowing electrons to flow into the metal nanoparticles. The Schottky barrier makes it difficult for the inflowing electrons to return to the transition metal dichalcogenide thin film, suppressing recombination with carriers and improving the electron lifetime.

[0022] Specifically, the particle size of these nano-sized metal nanoparticles is preferably 2 nm or more and 50 nm or less. The lower limit is set to 2 nm because excessively small metal nanoparticles are difficult to form. On the other hand, metal nanoparticles exceeding 50 nm are not preferred because they increase the Schottky barrier and make the depletion layer thicker than necessary, thereby eliminating the effect of injecting hot electrons into the semiconductor layer. Furthermore, the average particle size of the metal nanoparticles is more preferably 20 nm or more and 50 nm or less. This is because this allows for more effective formation of local Schottky bonds between the metal nanoparticles and the transition metal dichalcogenide thin film.

[0023] The metal N constituting the metal nanoparticles is preferably a metal having a work function larger than the band gap of the transition metal dichalcogenide (e.g., MX2:PtSe2) constituting the thin film. By joining a metal with a large work function, the above-mentioned carrier trap suppression effect of the Schottky junction becomes more pronounced. The increase in local surface electric field due to the formation of the Schottky junction and the resulting increase in the width and height of the depletion layer enhance the spatial separation between electrons excited by light energy and carriers, thereby extending the electron lifetime. By modifying the transition metal dichalcogenide thin film with metal nanoparticles having a large work function, the above effect can be effectively expressed, increasing the photocurrent.

[0024] Representative band gaps of the preferred transition metal dichalcogenides listed above are PtSe2 (1.20 eV (single layer) to 0.21 eV (double layer)), PtS2 (2.66 eV (single layer) to 0.25 eV (double layer)), PdSe2 (2.55 eV (single layer) to 1.89 eV (double layer)), and PtS2 (1.28 eV (single layer) to 1.03 eV (double layer)). The metal N in the present invention is preferably a metal having a work function of 3.0 eV or more, more preferably a metal having a work function of 4.0 eV or more.

[0025] Preferable specific examples of metal N include noble metals. Noble metals tend to have a large work function. Furthermore, because noble metals have excellent environmental resistance, they can exist stably even in a state with a high specific surface area, such as nanoparticles, making noble metal nanoparticles preferable. Suitable noble metals include Au, Ag, Pt, Pd, Ir, and Ru. The work functions of these noble metals are known to be Au: 5.47 eV, Ag: 4.64 eV, Pt: 5.64 eV, Pd: 4.9 eV, Ir: 5.35 eV, and Ru: 4.68 eV. However, metals other than noble metals, such as W, Mo, and Ni, with relatively high work functions, may also be used as metal N depending on the application. The work functions of these metals are known to be W: 4.52 eV, Mo: 4.45 eV, and Ni: 5.15 eV.

[0026] The metal N constituting the metal nanoparticles that modify the surface of the transition metal dichalcogenide thin film may be the same metal element as the metal M constituting the transition metal dichalcogenide thin film, or may be a different metal element.

[0027] (A-3-2) Surface morphology of thin films modified with metal nanoparticles The metal nanoparticles described above preferentially modify defects on the surface of the transition metal dichalcogenide thin film. Therefore, the semiconductor material according to the present invention has a surface morphology in which microscopic particulate irregularities are formed. As will be described later, defect sites on the thin film surface have high surface energy, and fine metal nanoparticles preferentially bond to these high-surface-energy sites. Therefore, by supplying an appropriate amount of metal nanoparticles to the thin film surface at an appropriate rate, the defect sites are preferentially modified. However, as mentioned above, preferentially modifying defects is not limited to a state in which metal nanoparticles modify only defects, and metal nanoparticles may also be bonded to regions other than defects. Furthermore, the metal nanoparticles may be individually dispersed or linked together.

[0028] However, modification with excessive metal nanoparticles will cause the thin film to become conductive and lose its semiconducting properties. For example, it is not desirable to modify the thin film surface with metal nanoparticles so that the entire surface or a similar state is covered with the metal nanoparticles. The amount of metal nanoparticles to be modified can be controlled by the ratio (density) of the metal nanoparticles to the surface area of ​​the thin film.

[0029] Specifically, when observing the surface of a thin film made of a transition metal dichalcogenide modified with metal nanoparticles, the area ratio of the total area of ​​the metal nanoparticles on the thin film (projected area on the thin film surface) to the area of ​​the observation field region is preferably 5% or more. This is because if it is less than 5%, the effect of modification by the metal nanoparticles is difficult to achieve. The lower limit of this area ratio takes into consideration application to transition metal dichalcogenide thin film surfaces that contain very few defects. On the other hand, if the area ratio of the metal nanoparticles is excessively high, as mentioned above, the thin film will become conductive and lose its function as a semiconductor material. Therefore, the area ratio of the metal nanoparticles is preferably 20% or less.

[0030] A specific method for measuring the area ratio of metal nanoparticles is preferably to observe the surface of a thin film made of a transition metal dichalcogenide modified with metal nanoparticles using a scanning electron microscope at a magnification of 50,000 to 100,000 times, based on the observation field area of ​​a backscattered electron image. The reason for this magnification is that if the magnification is too low, it is impossible to observe the lattice defects and metal nanoparticles, and if the magnification is too high, there will be a bias in the distribution of the lattice defects and metal nanoparticles in the observation field area, resulting in variations in the observation results.

[0031] (A-4) Specific uses of the semiconductor material according to the present invention The semiconductor material according to the present invention is applicable as a general semiconductor material, and its applications are not particularly limited. For example, it can be used as a semiconductor material for a wide range of applications, such as photoelectric conversion elements, light-receiving elements, field-effect transistors, optical sensors, photodetectors, and magneto-optical memory elements. In particular, the present invention is suitable as an optical semiconductor material applied to optical devices, and is useful in applications such as photoelectric conversion elements. More specifically, the present invention is suitable as a light-receiving element, and since it can be used in the near-infrared region (wavelength 0.7 to 3 μm) and has excellent light-receiving sensitivity, it is suitable for a light-receiving element for LIDAR applications.

[0032] (B) The method for producing a semiconductor material according to the present invention Next, a method for producing a semiconductor material according to the present invention will be described. As described above, the present invention is characterized by modifying the surface of a thin film made of a transition metal dichalcogenide with metal nanoparticles. While the step of modifying metal nanoparticles is essential, there are no limitations on the steps before and after that, that of forming a transition metal dichalcogenide thin film, or on the steps after the metal nanoparticle modification. Therefore, the method for producing a semiconductor material according to the present invention is a method for producing a semiconductor material that includes a step of forming a thin film made of transition metal dichalcogenide MX2 on a substrate (film formation step) and a step of modifying the surface of the thin film with metal nanoparticles made of metal N (modification step), and is characterized by using atomic layer deposition for the step of modifying the metal nanoparticles. Each step will be described below.

[0033] (B-1) Transition metal dichalcogenide thin film deposition process The method for forming a transition metal dichalcogenide thin film on a substrate is not particularly limited, and conventional methods for producing transition metal dichalcogenides can be used. Examples of methods for producing transition metal dichalcogenides include a metal film reaction method in which a transition metal thin film formed on a substrate is heat-treated in a chalcogen element atmosphere (such as sulfur gas or selenium gas) to form a chalcogenide, as well as thin film formation processes such as sputtering (reactive sputtering), physical vapor deposition methods such as vacuum deposition, and chemical vapor deposition methods such as chemical vapor deposition (CVD) and atomic layer deposition (ALD). In the present invention, the latter physical vapor deposition and chemical vapor deposition methods are preferred. Chemical vapor deposition is a particularly preferred film formation method, as chemical vapor deposition can efficiently produce a transition metal dichalcogenide thin film with a uniform target composition (MX2).

[0034] (B-2) Metal nanoparticle modification process Defects on the surface of the transition metal dichalcogenide thin film formed as described above are modified with metal nanoparticles. This metal nanoparticle modification process uses atomic layer deposition (ALD). Atomic layer deposition is a thin film formation process that repeats the following cycles: an adsorption step in which a source gas containing a precursor consisting of a complex of the metal to be modified is brought into contact with the surface of the workpiece, causing the precursor to adsorb onto the surface of the workpiece; a first evacuation step in which excess source gas is exhausted; a reaction step in which the precursor adsorbed on the surface of the workpiece reacts with a reactive gas on the surface to form metal nanoparticles; and a second evacuation step in which excess reactive gas is exhausted.

[0035] Atomic layer deposition is a film formation method characterized by its ability to deposit films in single-atom layer units and to control film thickness with high precision. The inventors' determination to use atomic layer deposition for the modification of metal nanoparticles stems from the aforementioned characteristics of this process. In addition, they focused on the relationship between the surface state of defect-containing transition metal dichalcogenide thin films and the behavior of unreacted precursor molecules (metal complex molecules). In transition metal dichalcogenide thin films, defects that disrupt the film's regularity have high surface energy. Unreacted precursor molecules introduced into a reactor and diffusing on the substrate tend to preferentially adsorb to high-surface-energy sites. The interaction between these defect sites and precursor molecules effectively contributes to the preferential modification of defects in transition metal dichalcogenide thin films, which is the objective of the present invention.

[0036] In contrast, chemical vapor deposition (CVD), which is also a chemical vapor deposition method like atomic layer deposition and uses the same precursors to form films, is a method of depositing metal precipitated by heat, reactive gases, etc. onto a substrate to form a film, and is therefore poor at selectively modifying metal nanoparticles as described above. Furthermore, physical vapor deposition methods such as sputtering are methods of depositing scattered metal particles onto a substrate by imparting momentum, etc., making it difficult to selectively modify the metal nanoparticles of the present invention.

[0037] The metal nanoparticle modification process of the present invention basically follows the general atomic layer deposition method, with the supply and discharge of the precursor gas and the supply and discharge of the reactant gas forming one deposition cycle, and is performed by repeating this cycle. The precursor of the metal nanoparticles is a compound (complex) that essentially contains the metal N that constitutes the metal nanoparticles. Metal complexes commonly used in chemical vapor deposition can be used. For example, for platinum, organic platinum compounds such as dimethyl(N,N-dimethyl-3-butan-1-amine-N)platinum (DDAP), 1,5-hexadienedimethylplatinum (HDMP), (trimethyl)methylcyclopentadienylplatinum (MeCpPtMe3), and bis(acetylacetonato)platinum (Pt(acac)2) can be used. For palladium, organic palladium compounds such as bis(hexafluoroacetylacetonato) (Pd(hfac)2), cyclopentadienylallylpalladium (CpPd(allyl)), and bis(methylallyl)palladium (Pd(Meallyl)2) are available. For ruthenium, organic ruthenium compounds such as dicarbonyl-bis(5-methyl-2,4-hexanedionato)ruthenium, hexacarbonyl[methyl-(1-methylpropyl)-butene-aminato]diruthenium, and dodecacarbonyltriruthenium (DCR) are available. For gold, trimethylphosphinotrimethylgold is available. For iridium, organic iridium compounds such as tris(acetylacetonato)iridium (Ir(acac)3) and (cyclohexadienyl)methylcyclopentadienyliridium ((MeCp)Ir(CHD)) are used. For silver, organic silver compounds such as triethylphosphine(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato)silver(I) (Ag(fod)(PEt3)) and 1-5 cyclooctadienehexafluoroacetylacetonatesilver(I) ([(hfac)(1,5-COD)Ag]) are used.

[0038] In atomic layer deposition, a metal complex precursor is vaporized and supplied to the substrate along with an appropriate carrier gas. The carrier gas is typically an inert gas such as argon or nitrogen. The precursor molecules selectively adsorb onto surface defects of the transition metal dichalcogenide thin film. The excess precursor gas is then vented from the reactor.

[0039] After adsorbing a precursor onto the surface of a transition metal dichalcogenide thin film, a reactive gas is introduced to form metal nanoparticles at the defect sites. The reactive gas is determined by the type and reactivity of the precursor metal complex, but typically includes reducing gases such as hydrogen, ammonia, and hydrazine, and oxidizing gases such as oxygen and ozone. Inert gases such as nitrogen can also be used as reactive gases by converting them into plasma using an assisted plasma. The assisted plasma may be used for reducing gases or oxidizing gases. After the reactive gas is supplied, excess gas is discharged.

[0040] The above process constitutes one cycle, and by repeating it multiple times, a predetermined amount of metal nanoparticles is modified onto the surface of the transition metal dichalcogenide thin film. The processing temperature in this modification process is set to 100°C or higher and 350°C or lower depending on the precursor used, and is mainly determined by heating the substrate.

[0041] In the present invention, the amount (density) of metal nanoparticles modifying the surface of the transition metal dichalcogenide thin film can be adjusted by the supply rates of precursor and reactive gas and the number of cycles in the atomic layer deposition method described above. As an example of conditions, the precursor is transported into the reaction vessel using an inert gas as a carrier gas at 5 sccm to 100 sccm. The supply rate of the reactive gas is 100 to 300 sccm. As described above, the reactive gas may be a reducing gas such as hydrogen, ammonia, or hydrazine, or an oxidizing gas such as oxygen or ozone, but hydrogen or oxygen is preferred. The reaction vessel and substrate are preferably heated to 100°C to 350°C.

[0042] The number of cycles is set to achieve an appropriate nanoparticle coverage. For example, when DDAP is used to modify platinum nanoparticles, the number of cycles can be 5 to 100 if hydrogen is used as the reactive gas, and 10 to 200 if oxygen is used as the reactive gas.

[0043] The semiconductor material of the present invention can be manufactured by the metal nanoparticle modification process described above. Furthermore, plasma treatment or acid treatment can be optionally performed as a treatment after the metal nanoparticle modification process. The semiconductor material manufactured by the above process can be made into a semiconductor element by adding electrodes as needed. [Effects of the Invention]

[0044] As described above, the semiconductor material according to the present invention has superior light-receiving sensitivity to conventional transition metal dichalcogenides and is useful as a light-receiving element. Furthermore, the semiconductor material according to the present invention and its manufacturing method satisfy all of the requirements of high light-receiving sensitivity, low manufacturing cost, and use at room temperature, making it particularly suitable as a light-receiving element for LIDAR. [Brief explanation of the drawings]

[0045] [Figure 1] 1 is an SEM image showing the surface morphology of the semiconductor material (Pt / PtSe 2 ) manufactured in the first embodiment and Comparative Example 1. [Figure 2] FIG. 2 is a graph showing the IR response characteristics of semiconductor materials according to the first embodiment and Comparative Example 1. [Figure 3] FIG. 2 is a graph showing carrier lifetime characteristics of semiconductor materials according to the first embodiment and Comparative Example 1. [Figure 4] FIG. 10 is a graph showing the IR response characteristics of semiconductor materials according to the second embodiment and Comparative Example 2. [Figure 5] FIG. 10 is a graph showing carrier lifetime characteristics of semiconductor materials according to the second embodiment and Comparative Example 2. [Figure 6] 10 is an SEM image showing the surface morphology of the semiconductor material (Ru / PtSe2) produced in the third embodiment. [Figure 7]FIG. 10 is a diagram showing the IR response characteristics of the semiconductor material of the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0046] First embodiment Hereinafter, an embodiment of the present invention will be described. In this embodiment, a thin film made of PtSe2 as a transition metal dichalcogenide was formed on a substrate. Then, Pt particles as metal nanoparticles were modified on the surface of the thin film to produce a semiconductor material. The photoresponse characteristics of the produced semiconductor material to near-infrared light were evaluated, and the surface morphology was investigated.

[0047] [Semiconductor material manufacturing] Formation of transition metal dichalcogenide thin films A SiO2 glass substrate (20 x 20 mm, 1.5 mm thick) was prepared as the substrate, and a PtSe2 thin film was formed on this substrate by CVD (thermal CVD). First, the substrate was placed in a CVD apparatus (hot-wall horizontal CVD apparatus), and 5 g of selenium powder was placed upstream of the substrate. The temperatures of the substrate and selenium powder were independently controllable. Before film formation, the reactor was purged with argon gas (200 sccm).

[0048] A platinum complex (dimethyl(N,N-dimethyl-3-butan-1-amine-N)platinum (DDAP)) was used as the thin film raw material. The platinum complex was heated and vaporized, and then introduced into the reactor together with a carrier gas. The vaporized platinum complex was decomposed on the substrate, and the platinum reacted with selenium to precipitate PtSe2, forming a thin film. The film formation conditions were as follows. The thickness of the PtSe2 thin film formed on the substrate in this film formation process was 4 nm. Note that this PtSe2 thin film is a semiconductor material that exhibits n-type semiconductor properties. ·Raw material heating temperature: 67℃ Carrier gas: Argon / 10sccm Substrate temperature / Selenium powder heating temperature: 400℃ / 220℃ Deposition time: 15 minutes

[0049] Metal nanoparticle modification process Next, the surface of the PtSe2 thin film formed above was modified with Pt nanoparticles by atomic layer deposition. The CVD apparatus used was the same as that used to form the PtSe2 thin film. The platinum complex used as the precursor (raw material gas) for the Pt nanoparticles was the same DDAP as above. The substrate with the PtSe2 thin film formed on it was placed in a reactor, which was then purged with argon (80 sccm), and the following steps (1) to (4) were performed as one cycle. (1) Introduction of raw material gas ·Raw material heating temperature: 67℃ Carrier gas: Argon / 10sccm Introduction time: 4 seconds (2) Raw material gas discharge Purge with argon gas (80sccm) Introduction time: 5 seconds (3) Reactant gas introduction Reactive gas: pure oxygen / 150sccm Introduction time: 7 seconds (4) Reaction gas exhaust Purge with argon gas (80sccm) Introduction time: 5 seconds

[0050] In this embodiment, the above steps (1) to (4) were repeated 10 times to modify the surface of the PtSe2 thin film with Pt nanoparticles, thereby producing a semiconductor material.

[0051] Comparative Example 1 As a comparative example for the first embodiment described above, a semiconductor material without modification of the surface defects of the PtSe2 thin film was produced. In this comparative example, a PtSe2 thin film was formed on a substrate in the same manner as in the first embodiment, and then the semiconductor material was produced without modification with Pt nanoparticles.

[0052] [Measurement of average particle size and area ratio of metal nanoparticles] The average particle size and area ratio of Pt nanoparticles on the surface of the semiconductor material of the first embodiment were measured. Figure 1 shows an example of an SEM image of the semiconductor material (Pt / PtSe2) manufactured in the first embodiment. To measure the average particle size of Pt nanoparticles, the surface was observed using a scanning electron microscope (SEM) at 50,000x magnification. The particle size and area ratio of the Pt nanoparticles were then determined based on the SEM image. For particle size measurement, 50 particles were randomly selected from the image, and the long and short diameters of each were measured. The average particle size was calculated by averaging these values. The area ratio of the metal nanoparticles was calculated as a percentage (%) of the area occupied by the metal nanoparticles in the observed region of the image. This calculation was performed using image analysis software (name: ImageJ). The image was converted to 8-bit resolution and then binarized. The average particle size of the nanoparticles and the area ratio were calculated from the area of ​​all nanoparticles and the area of ​​the measured region. The average particle size of the Pt nanoparticles was 22.73 nm. The area ratio of Pt nanoparticles was 12.54%.

[0053] [Evaluation of photoresponse of semiconductor materials] The photoresponse to near-infrared rays was measured for the semiconductor materials of the first embodiment and Comparative Example 1 prepared above. The measurement method involved forming a comb-shaped electrode on the surface of the semiconductor material, irradiating it with near-infrared rays, and measuring the photocurrent at room temperature using a multimeter. The comb-shaped electrode was formed by patterning a Ti film (5 nm thick) and an Au film (40 nm thick) in this order onto the surface of a PtSe2 thin film modified with Pt nanoparticles. The wavelength of the irradiated near-infrared rays was 940 nm. The near-infrared rays were irradiated intermittently for 20 seconds with 40-second intervals. A bias voltage of 0.5 V was applied for the four-terminal method. The measurement results are shown in Figure 2.

[0054] The measurement results of this response characteristic showed that the semiconductor material (first embodiment) including the PtSe2 thin film modified with Pt nanoparticles can generate approximately five times the photocurrent compared to the semiconductor material (comparative example 1) including the conventional PtSe2 thin film. This confirmed that modifying the PtSe2 thin film with Pt nanoparticles results in an optical semiconductor material with excellent light-receiving sensitivity.

[0055] [Carrier lifetime evaluation by open circuit voltage decay method] The carrier lifetime of the PtSe2 thin film modified with Pt nanoparticles was measured using the open circuit voltage decay method (OCVD method). The electrode of the PtSe2 thin film modified with Pt nanoparticles patterned in a comb shape was connected to a probe station system. As in the evaluation of photoresponse, infrared light of 940 nm was irradiated to induce the photoelectric effect. The relationship between the voltage drop and time when infrared light irradiation was stopped was then measured using the probe station, and the carrier lifetime τ was calculated using the following equation.

[0056]

number

[0057] FIG. 3 shows the results of measuring carrier lifetime characteristics. From these test results, the electron lifetime of the semiconductor material including the PtSe2 thin film modified with Pt nanoparticles according to the first embodiment was 38.1 picoseconds. On the other hand, the electron lifetime of the semiconductor material including the PtSe2 thin film without conventional metal nanoparticle modification was 1.96 picoseconds. From these results, it can be said that the electron lifetime was extended as a result of suppressing carrier traps due to the modification with Pt nanoparticles. From these evaluation results regarding the electron lifetime, it was confirmed that modifying the PtSe2 thin film with Pt nanoparticles can result in an optical semiconductor material with excellent light-receiving sensitivity.

[0058] Second embodiment : In this embodiment, a thin film of PdSe2 was formed on a substrate as a transition metal dichalcogenide thin film, and Pt particles were attached to the surface of the thin film as metal nanoparticles to produce semiconductor materials. As in the first embodiment, the surface morphology of each semiconductor material was investigated and its semiconducting properties were evaluated.

[0059] [Semiconductor material manufacturing] Formation of transition metal dichalcogenide thin films In this embodiment, a Pd thin film was first formed on a substrate, and then selenized to produce a transition metal dichalcogenide thin film (PdSe thin film). An SiO glass substrate (dimensions: 20 × 20, thickness: 1.5 mm) was prepared as the substrate, and a Pd thin film was formed on this substrate by vacuum evaporation (thermal evaporation). The substrate was set on the top of a vacuum chamber, and a Pd evaporation source was placed on a tungsten boat at the bottom of the chamber opposite to the substrate. -6 The pressure inside the chamber was reduced to below the order of Pa. Then, a current was passed through the tungsten boat, and the Pd evaporation source was heated and vaporized by resistance heating, forming a Pd film on the opposing substrate. A film thickness meter was used to deposit the Pd thin film until it reached a thickness of 1 nm.

[0060] Next, for selenization, the Pd-deposited substrate was placed in a tubular furnace, and 5 g of selenium powder was placed upstream of the substrate. At this time, the temperatures of the substrate and selenium powder could be controlled. Before film formation, the reactor was purged with argon gas (60 sccm). The film formation conditions were as follows: The thickness of the PdSe2 thin film formed on the substrate through this series of steps was 4 nm. Note that this PdSe2 thin film is a semiconductor material that exhibits n-type semiconductor properties. Argon gas flow rate: 60sccm Substrate temperature / Selenium powder heating temperature: 400℃ / 220℃ Selenization time: 90 minutes

[0061] Metal nanoparticle modification process Next, the surface of the PdSe2 thin film formed above was modified with Pt nanoparticles by atomic layer deposition. The equipment used was the same CVD equipment as that used in the first embodiment to form the PtSe2 thin film and modify the Pt particles. The Pt complex used as the precursor (raw material gas) for the Pt nanoparticles was the same DDAP as above. The substrate on which the PtSe2 thin film was formed was placed in the reactor, and after purging with argon (80 sccm), the following steps (1) to (4) were performed as one cycle. The substrate (1) Introduction of raw material gas ·Raw material heating temperature: 67℃ Carrier gas: Argon / 10sccm Introduction time: 4 seconds (2) Raw material gas discharge Purge with argon gas (80sccm) Introduction time: 5 seconds (3) Reactant gas introduction Reactive gas: pure hydrogen / 150sccm Introduction time: 7 seconds (4) Reaction gas exhaust Purge with argon gas (80sccm) Introduction time: 5 seconds

[0062] In this embodiment, the above steps (1) to (4) were repeated 10 times to modify the surface of the PdSe2 thin film with Pt nanoparticles, thereby producing a semiconductor material.

[0063] Comparative Example 2 As Comparative Example 2 for the second embodiment described above, a semiconductor material without modification of the surface defects of the PdSe thin film was produced. In the second embodiment described above, after the PdSe thin film was formed on the substrate, the semiconductor material was produced without modification with Pt nanoparticles.

[0064] [Measurement of average particle size and area ratio of metal nanoparticles] The average particle size and area ratio of Pt nanoparticles on the surface of the semiconductor material of the second embodiment were measured. The method for measuring the average particle size and area ratio of the Pt nanoparticles was the same as in the first embodiment. As a result, the average particle size of the Pt nanoparticles was 7.98 nm. The area ratio of the Pt nanoparticles was 10.16%.

[0065] [Evaluation of photoresponse of semiconductor materials] The photoresponse to near-infrared rays was measured for the semiconductor materials of the second embodiment and comparative example 2 prepared above. The measurement method and electrode formation method were the same as those of the first embodiment and comparative example 1 (near-infrared wavelength: 940 nm). The measurement results are shown in Figure 4.

[0066] 4, it can be seen that the semiconductor material including the PdSe2 thin film modified with Pt nanoparticles (second embodiment) can generate approximately five times the photocurrent compared to the semiconductor material including the conventional PdSe2 thin film (comparative example 2). This confirms that even in the case of a PdSe2 thin film, modifying it with Pt nanoparticles can result in an optical semiconductor material with excellent light-receiving sensitivity.

[0067] [Carrier lifetime evaluation by open circuit voltage decay method] As in the first embodiment, the carrier lifetime of a PdSe2 thin film modified with Pt nanoparticles was measured using the OCVD method. The results are shown in Figure 5. As can be seen from Figure 5, the semiconductor material including the PdSe2 thin film modified with Pt nanoparticles of the second embodiment had a carrier lifetime of 77.9 picoseconds. In contrast, the semiconductor material including the PdSe2 thin film without metal nanoparticles of Comparative Example 2 had a carrier lifetime of 7.18 picoseconds. In this embodiment as well, an increase in the electron lifetime due to modification with Pt nanoparticles was confirmed.

[0068] Third embodiment In this embodiment, a thin film made of PtSe2 was formed on a substrate as a transition metal dichalcogenide thin film, and the surface of the thin film was modified with Ru particles as metal nanoparticles to produce a semiconductor material. The photoresponse characteristics of the semiconductor material to near-infrared light were then evaluated, and the surface morphology was investigated.

[0069] [Semiconductor material manufacturing] Formation of transition metal dichalcogenide thin films Using the same SiO2 glass substrate as in the first embodiment as a base material, a PtSe2 thin film was formed by CVD in the same manner as in the first embodiment. A platinum complex (DDAP) was used as the thin film raw material. The platinum complex was heated and vaporized and introduced into a reactor together with a carrier gas. The vaporized platinum complex was decomposed on the substrate, and the platinum reacted with selenium to precipitate PtSe2, forming a thin film. The film formation conditions were the same as in the first embodiment, and the PtSe2 thin film had a thickness of 4 nm.

[0070] Metal nanoparticle modification process The surface of the PtSe2 thin film formed above was modified with Ru nanoparticles by atomic layer deposition. The CVD apparatus used was the same as that used to form the PtSe2 thin film. Furthermore, tricarbonyl(trimethylenemethane)ruthenium (Ru(TMM)(CO)3)) was used as the Ru complex that served as the precursor (raw material gas) for the Ru nanoparticles. The substrate with the PtSe2 thin film formed on it was placed in a reactor, which was then purged with argon (100 sccm), and the following steps (1) to (4) were repeated as one cycle. (1) Introduction of raw material gas ·Raw material heating temperature: 10℃ Carrier gas: Argon / 50sccm Introduction time: 10 seconds (2) Raw material gas discharge Purge with argon gas (100sccm) Introduction time: 10 seconds (3) Reactant gas introduction Reactive gas: pure oxygen / 50sccm Introduction time: 10 seconds (4) Reaction gas exhaust Purge with argon gas (100sccm) Introduction time: 10 seconds

[0071] In this embodiment, the above steps (1) to (4) were repeated 50 times to modify the surface of the PtSe2 thin film with Ru nanoparticles, thereby producing a semiconductor material.

[0072] [Measurement of average particle size and area ratio of metal nanoparticles] The average particle size and area ratio of Ru nanoparticles on the surface of the semiconductor material of the third embodiment were measured. The average particle size and area ratio of Ru nanoparticles were measured based on surface observation using an SEM, as in the first embodiment. The average particle size of the Ru nanoparticles in this embodiment was 12.47 nm. The area ratio of the Ru nanoparticles was 1.98%. Figure 6 shows an example of an SEM image of the semiconductor material (Ru / PtSe2) produced in the third embodiment.

[0073] [Evaluation of photoresponse of semiconductor materials] The photoresponse to near-infrared rays of the semiconductor material of the third embodiment prepared above was measured. The measurement method and electrode formation method were the same as those of the first embodiment, and the wavelengths of the irradiated near-infrared rays were 740 nm, 850 nm, and 940 nm. The measurement results are shown in Figure 7. Figure 7 also shows the results of a semiconductor material not modified with Ru particles (bare PtSe2 thin film: Comparative Example 1) in addition to the semiconductor material of this embodiment (Ru / PtSe2).

[0074] The measurement results in Figure 7 show that the semiconductor material including the PtSe2 thin film modified with Ru nanoparticles (third embodiment) can generate a higher photocurrent in all wavelength ranges than the semiconductor material including only the PtSe2 thin film (comparative example 1). In this embodiment, approximately eight times the photocurrent can be generated. These results confirm that modification with Ru nanoparticles can also improve the light-receiving sensitivity of the transition metal dichalcogenide thin film. [Industrial Applicability]

[0075] As explained above, the semiconductor material and its manufacturing method according to the present invention satisfy all the requirements of high light receiving sensitivity, low manufacturing cost, and use at room temperature, and are useful as light receiving elements. In particular, because it has significantly better light receiving sensitivity in the near-infrared region than conventional transition metal dichalcogenides, it is expected to contribute to further improvement of measurement accuracy as a material for light receiving elements for LIDAR applications.

Claims

1. a substrate; and an MX formed on the substrate. ２ (M is a transition metal, and X is a chalcogen atom other than oxygen), and a thin film made of a transition metal dichalcogenide represented by the formula: (M is a transition metal, and X is a chalcogen atom other than oxygen), and the thin film comprises metal nanoparticles made of metal N and modifying a surface of the thin film; The semiconductor material is characterized in that the metal nanoparticles have an average particle size of 2 nm or more and 50 nm or less.

2. The work function of the metal N constituting the metal nanoparticles is ２ 2. The semiconductor material of claim 1, wherein the band gap is greater than 1.

3. Transition metal dichalcogenide MX ２ 3. The semiconductor material according to claim 1, wherein the transition metal M is either Pt or Pd.

4. Transition metal dichalcogenide MX ２ 4. The semiconductor material according to claim 1, wherein the chalcogen X is any one of sulfur, selenium, and tellurium.

5. 5. The semiconductor material according to claim 1, wherein the metal N constituting the metal nanoparticles is a noble metal.

6. 6. The semiconductor material according to claim 1, wherein, when observing the surface of a thin film made of a transition metal dichalcogenide modified with metal nanoparticles, the area ratio occupied by the metal nanoparticles in the observation field of view is 5% or more and 20% or less.

7. 7. The semiconductor material according to claim 1, wherein the substrate is made of any one of glass, quartz, silicon, carbon, ceramics, and metal.

8. A light-receiving element comprising the semiconductor material according to any one of claims 1 to 7.

9. A method for producing a semiconductor material according to any one of claims 1 to 7, comprising: Transition metal dichalcogenide MX on a substrate ２ and modifying the surface of the thin film with metal nanoparticles made of metal N, A method for producing a semiconductor material, characterized in that atomic layer deposition is used in the step of modifying the metal nanoparticles.

10. Thin film MX made of transition metal dichalcogenide ２ 10. The method for producing a semiconductor material according to claim 9, wherein either physical vapor deposition or chemical vapor deposition is used as the step of forming the semiconductor material.

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