SEMICONDUCTOR MATERIAL INCLUDING TRANSITION METAL DICHALCOGENIDE THIN FILM AND METHOD FOR PRODUCING SAME, AND LIGHT-RECEIVING ELEMENT INCLUDING THE SEMICONDUCTOR MATERIAL

Abstract

The present invention relates to a semiconductor material including a thin film formed on a base material, the thin film including a transition metal dichalcogenide represented by MX.sub.2, wherein M is a transition metal and X is a chalcogen atom except oxygen. In the present invention, the thin film is modified with metal nanoparticles including metallic N, whereby defect portions on the surface of the transition metal dichalcogenide thin film are modified to thereby improve the semiconductor characteristics of the thin film. These metal nanoparticles are preferably the nanoparticles of a precious metal. The transition metal M in the transition metal dichalcogenide thin film on the base material is preferably a sulfide, selenide or telluride of Pt or Pd. In the step of modifying with the metal nanoparticles, an atomic layer deposition method (ALD) is particularly preferably applied.

Claims

1. A semiconductor material comprising: a base material; and a thin film formed on the base material and comprising a transition metal dichalcogenide represented by MX.sub.2, wherein M is a transition metal and X is a chalcogen atom except oxygen, wherein the semiconductor material comprises metal nanoparticles comprising metallic N and modifying a surface of the thin film.

2. The semiconductor material according to claim 1, wherein an average particle diameter of the metal nanoparticles is 2 nm or more and 50 nm or less.

3. The semiconductor material according to claim 1, wherein a work function of the metallic N of the metal nanoparticles is larger than a band gap of the transition metal dichalcogenide MX.sub.2 of the thin film.

4. The semiconductor material according to any one of claims 1 to 3, wherein the transition metal M of the transition metal dichalcogenide MX.sub.2 is Pt or Pd.

5. The semiconductor material according to any one of claims 1 to 4, wherein the chalcogen X of the transition metal dichalcogenide MX.sub.2 is sulfur, selenium, or tellurium.

6. The semiconductor material according to any one of claims 1 to 5, wherein the metallic N of the metal nanoparticles is a precious metal.

7. The semiconductor material according to any one of claims 1 to 6, wherein, when the surface of the thin film comprising the transition metal dichalcogenide and modified with the metal nanoparticles is observed, a percentage of the area of the metal nanoparticles is 5% or more and 20% or less of an observation field region.

8. The semiconductor material according to any one of claims 1 to 7, wherein the base material comprises glass, quartz, silicon, carbon, ceramic, or metal.

9. A light-receiving element comprising the semiconductor material defined in any one of claims 1 to 8.

10. A method for producing the semiconductor material defined in any one of claims 1 to 8, the method comprising: forming the thin film comprising the transition metal dichalcogenide MX.sub.2 on the base material; and modifying the surface of the thin film with the metal nanoparticles comprising the metallic N, wherein an atomic layer deposition method is used for modifying with the metal nanoparticles.

11. The method for producing the semiconductor material according to claim 10, wherein a physical deposition method or a chemical deposition method is used for forming the thin film comprising the transition metal dichalcogenide MX.sub.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] FIG. 1 is SEM images showing the surface morphologies of semiconductor materials (Pt/PtSe.sub.2) manufactured in First Embodiment and Comparative Example 1;

[0048] FIG. 2 is a view showing the IR response characteristics of the semiconductor materials of First Embodiment and Comparative Example 1;

[0049] FIG. 3 is a view showing the carrier lifetime characteristics of the semiconductor materials of First Embodiment and Comparative Example 1;

[0050] FIG. 4 is a view showing the IR response characteristics of semiconductor materials of Second Embodiment and Comparative Example 2;

[0051] FIG. 5 is a view showing the carrier lifetime characteristics of the semiconductor material of Second Embodiment and Comparative Example 2;

[0052] FIG. 6 is a SEM image showing the surface morphology of a semiconductor material (Ru/PtSe.sub.2) manufactured in Third Embodiment; and

[0053] FIG. 7 is a view showing the IR response characteristic of the semiconductor material of Third Embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] First Embodiment: Hereinafter, an embodiment of the present invention will be described. In the present embodiment, a thin film of PtSe.sub.2 as a transition metal dichalcogenide was formed on a base material. Then, the surface of the thin film was modified with Pt particles as metal nanoparticles to produce a semiconductor material. Regarding the manufactured semiconductor material, the photoresponsivity to near-infrared rays was evaluated and the surface morphology was studied.

[Production of Semiconductor Material]

Formation of Transition Metal Dichalcogenide Thin Film

[0055] A SiO.sub.2 glass substrate (dimensions: 2020, thickness: 1.5 mm) was provided as a base material, and a PtSe.sub.2 thin film was formed on this base material by a CVD method (thermal CVD). First, the substrate was set in a CVD device (hot wall-type horizontal CVD device), and 5 g of a selenium powder was disposed upstream of the substrate. The substrate temperature and the temperature of the selenium powder were each controllable. The inside of a reactor was purged with an argon gas (200 sccm) before film formation.

[0056] Then, a platinum complex (dimethyl(N,N-dimethyl-3-butane-1-amine-N) platinum (DDAP)) was used as a raw material for a thin film. The platinum complex was heated to be vaporized, and introduced together with a carrier gas into the reactor. The platinum complex vaporized was decomposed on the substrate, and platinum and selenium were reacted with each other to precipitate PtSe.sub.2, thereby forming a thin film. The conditions for film formation were as described below. The film thickness of the PtSe.sub.2 thin film formed on the base material in this film formation step was 4 nm. This PtSe.sub.2 thin film is a semiconductor material showing an n-type semiconductor tendency. [0057] Heating temperature of raw material: 67 C. [0058] Carrier gas: Argon/10 sccm [0059] Temperature of substrate/heating temperature of selenium powder: 400 C./220 C. [0060] Film formation time: 15 minutes
Modification Step with Metal Nanoparticles

[0061] Next, the surface of the PtSe.sub.2 thin film formed above was modified with Pt nanoparticles by an atomic layer deposition method. The device used was the same as the CVD device used to form the PtSe.sub.2 thin film. In addition, as a platinum complex that served as a precursor (raw material gas) of Pt nanoparticles, the same DDAP as above was used. The substrate on which the PtSe.sub.2 thin film had been formed was placed in a reactor, and the reactor was purged with argon (80 sccm). Then, the following (1) to (4) was regarded as one cycle. [0062] (1) Introduction of raw material gas [0063] Heating temperature of raw material: 67 C. [0064] Carrier gas: Argon/10 sccm [0065] Introduction time: Four seconds [0066] (2) Exhaustion of raw material gas [0067] Purged with argon gas (80 sccm) [0068] Introduction time: Five seconds [0069] (3) Introduction of reaction gas [0070] Reaction gas: Pure oxygen/150 sccm [0071] Introduction time: Seven seconds [0072] (4) Exhaustion of reaction gas [0073] Purged with argon gas (80 sccm) [0074] Introduction time: Five seconds

[0075] In the present embodiment, 10 cycles each consisting of (1) to (4) above were performed to thereby modify the PtSe.sub.2 thin film with the Pt nanoparticles to manufacture a semiconductor material.

[0076] Comparative Example 1: As a comparative example with respect to First Embodiment described above, a semiconductor material was manufactured in which modification of surface defects in a PtSe.sub.2 thin film was not performed. In this comparative example, the semiconductor material was produced by forming the PtSe.sub.2 thin film on a substrate in the same manner as in First Embodiment and not performing modification with Pt nanoparticles.

[Measurement of Average Particle Diameter and Percentage of Area of Metal Nanoparticles]

[0077] For the Pt nanoparticles on the surface of the semiconductor material of First Embodiment, the average particle diameter and the percentage of the area were measured. FIG. 1 shows an example of a SEM image of the semiconductor material (Pt/PtSe.sub.2) manufactured in First Embodiment. In the measurement of the average particle diameter of the Pt nanoparticles, surface observation was performed with a scanning electron microscope (SEM) at a magnification of 50000. Then, the particle diameters and the percentage of the area of the Pt nanoparticles were obtained from the SEM image. In the measurement of the particle diameters, 50 particles were arbitrarily extracted from the image, the major axis and minor axis of each were measured, the average value thereof was regarded as the particle diameter, and the average particle diameter of the targeted particles was calculated. Regarding the percentage of the area of the metal nanoparticles, the percentage (%) of the area of the metal nanoparticles in an observation region in the image was calculated. This calculation was performed with image analysis software (name: ImageJ). As for analysis conditions, the image was converted to eight bits and binarized, and the percentage of the area was obtained from the average particle diameter of the nanoparticles, the area of all of the nanoparticles and the area of the measurement region. As a result, the average particle diameter of the Pt nanoparticles was 22.73 nm. The percentage of the area of the Pt nanoparticles was 12.54%.

[Evaluation of Photoresponsivity of Semiconductor Material]

[0078] Regarding the semiconductor materials of First Embodiment and Comparative Example 1 produced above, the photoresponsivity to near-infrared rays was measured. As for the measuring method, comb-shaped electrodes were formed on the surface of the semiconductor material; and then the resultant was irradiated with near-infrared rays, and a photocurrent was measured at room temperature using a multimeter. The comb-shaped electrodes were formed by sequentially patterning a Ti film (film thickness: 5 nm) and a Au film (film thickness: 40 nm) in a comb shape on the surface of the PtSe.sub.2 thin film modified with the Pt nanoparticles. The wavelength of the near-infrared rays used for the irradiation was 940 nm. The irradiation with the near-infrared rays was continuously performed for 20 seconds at 40-second intervals. In a four-point probe method, 0.5 V was loaded as a bias voltage. These measurement results are shown in FIG. 2.

[0079] From the measurement results of these response characteristics, it was found that the semiconductor material including the PtSe.sub.2 thin film modified with the Pt nanoparticles (First Embodiment) was capable of generating photocurrents approximately five times larger than those by the semiconductor material including a conventional PtSe.sub.2 thin film (Comparative Example 1). From this fact, it was confirmed that, when a PtSe.sub.2 thin film is modified with Pt nanoparticles, optical semiconductor materials become excellent in terms of light-receiving sensitivity.

[Evaluation of Carrier Lifetime by Open-Circuit Voltage Decay Method]

[0080] On the PtSe.sub.2 thin film modified with the Pt nanoparticles, the carrier lifetime was measured using the open-circuit voltage decay method (OCVD method). The electrodes patterned in the comb shape on the PtSe.sub.2 thin film modified with the Pt nanoparticles were connected to a probe station system. Irradiation with 940 nm infrared rays was performed as in the evaluation of the photoresponsivity to develop the effect of converting light to electricity. The relationship between the voltage drop at the time of stopping the irradiation with the infrared rays and the time was determined with the probe system, and a carrier lifetime t was calculated using the following formula.

[00001]$\begin{array}{cc}=\frac{k_{b}T}{e}{\left(\frac{\mathrm{dV}}{\mathrm{dt}}\right)}^{-1}& \left[\mathrm{Math}1\right]\end{array}$

[0081] FIG. 3 is a view showing the measurement results of the carrier lifetime characteristics. These test results show that the electron lifetime of the semiconductor material including the PtSe.sub.2 thin film modified with the Pt nanoparticles of First Embodiment was 38.1 picoseconds. On the other hand, the electron lifetime of the semiconductor material including the conventional PtSe.sub.2 thin film not modified with metal nanoparticles was 1.96 picoseconds. From these results, it is deemed that, as a result of suppression of carrier trapping by modification with the Pt nanoparticles, the lifetime of electrons becomes long. From this evaluation result regarding the electron lifetime, it was also confirmed that, when a PtSe.sub.2 thin film is modified with Pt nanoparticles, optical semiconductor materials having an excellent light-receiving sensitivity can be produced.

Second Embodiment

[0082] In the present embodiment, a thin film of PdSe.sub.2 as a transition metal dichalcogenide thin film was formed on a base material, and the surface of the thin film was modified with Pt particles as metal nanoparticles, thereby producing a semiconductor material. Regarding each semiconductor material, the surface morphology was studied and semiconductor characteristics were evaluated in the same manner as in First Embodiment.

[Manufacturing of Semiconductor Material]

Formation of Transition Metal Dichalcogenide Thin Film

[0083] In the present embodiment, first, a Pd thin film was formed on a base material and then selenized, thereby manufacturing a transition metal dichalcogenide thin film (PdSe.sub.2 thin film). A SiO.sub.2 glass substrate (dimensions: 2020, thickness: 1.5 mm) was provided as a base material, and a Pd thin film was formed on this base material by a vacuum deposition method (thermal deposition method). The substrate was set on the upper side in a vacuum chamber, and in the facing lower site in the chamber, a Pd deposition source was placed on a tungsten boat, followed by reducing the pressure in the chamber to 10-6 Pa order or less. After that, a current was caused to flow in the tungsten boat, and the Pd deposition source was heated by resistance heating to be vaporized, thereby forming a film of Pd on the facing substrate. At this time, deposition was performed until the film thickness of the Pd thin film reached 1 nm as measured using a film thickness meter.

[0084] Next, for selenization, the Pd-deposited substrate was set in a tubular furnace, and 5 g of a selenium powder was placed upstream of the substrate. At this time, the substrate temperature and the temperature of the selenium powder were each controllable. The inside of a reactor was purged with an argon gas (60 sccm) before film formation. The conditions for film formation were as described below. The film thickness of the PdSe.sub.2 thin film formed on the base material in this sequence of the steps was 4 nm. This PdSe.sub.2 thin film is a semiconductor material showing an n-type semiconductor tendency. [0085] Flow rate of argon gas: 60 sccm [0086] Temperature of substrate/heating temperature of selenium powder: 400 C./220 C. [0087] Selenization time: 90 minutes
Modification Step with Metal Nanoparticles

[0088] Next, the surface of the PdSe.sub.2 thin film formed above was modified with Pt nanoparticles by an atomic layer deposition method. The device used was the same as the CVD device used to form the PtSe.sub.2 thin film and also to modify the thin film with the Pt particles in First Embodiment. In addition, as a Pt complex that served as a precursor (raw material gas) of Pt nanoparticles, the same DDAP as above was used. The substrate on which the PtSe.sub.2 thin film had been formed was placed in a reactor, and the reactor was purged with argon (80 sccm). Then the following (1) to (4) was regarded as one cycle. Furthermore, the substrate [0089] (1) Introduction of raw material gas [0090] Heating temperature of raw material: 67 C. [0091] Carrier gas: Argon/10 sccm [0092] Introduction time: Four seconds [0093] (2) Exhaustion of raw material gas [0094] Purged with argon gas (80 sccm) [0095] Introduction time: Five seconds [0096] (3) Introduction of reaction gas. [0097] Reaction gas: Pure hydrogen/150 sccm [0098] Introduction time: Seven seconds [0099] (4) Exhaustion of reaction gas [0100] Purged with argon gas (80 sccm) [0101] Introduction time: Five seconds

[0102] In the present embodiment, 10 cycles each consisting of (1) to (4) above were performed to thereby modify the surface of the PdSe.sub.2 thin film with the Pt nanoparticles to manufacture a semiconductor material.

Comparative Example 2: As Comparative Example 2 with respect to Second

[0103] Embodiment described above, a semiconductor material was manufactured in which modification of surface defects in a PdSe.sub.2 thin film was not performed. The semiconductor material was produced by forming the PdSe.sub.2 thin film on a substrate and then not performing modification with Pt nanoparticles in Second Embodiment.

[Measurement of Average Particle Diameter and Percentage of Area of Metal Nanoparticles]

[0104] For the Pt nanoparticles on the surface of the semiconductor material of Second Embodiment, the average particle diameter and the percentage of the area were measured. The method for measuring the average particle diameter and the measurement of the percentage of the area of the Pt nanoparticles were the same as in First Embodiment. As a result, the average particle diameter of the Pt nanoparticles was 7.98 nm. The percentage of the area of the Pt nanoparticles was 10.16%.

[Evaluation of Photoresponsivity of Semiconductor Material]

[0105] On the semiconductor materials of Second Embodiment and Comparative Example 2 produced above, the photoresponsivity to near-infrared rays was measured. As for the measurement method and the method for electrode formation were the same as in First Embodiment and Comparative Example 1 (near-infrared ray wavelength: 940 nm). These measurement results are shown in FIG. 4.

[0106] From the measurement result of FIG. 4, it is found that the semiconductor material including the PdSe.sub.2 thin film modified with the Pt nanoparticles (Second Embodiment) was capable of generating photocurrents approximately five times larger than those by the semiconductor material including a conventional PdSe.sub.2 thin film (Comparative Example 2). From this fact, it was confirmed that, when a PdSe.sub.2 thin film is modified with Pt nanoparticles, optical semiconductor materials become excellent in terms of light-receiving sensitivity.

[Carrier Lifetime Evaluation by Open-Circuit Voltage Decay Method]

[0107] On the PdSe.sub.2 thin film modified with the Pt nanoparticles, the carrier lifetime was measured using the OCVD method in the same manner as in First Embodiment. The results are shown in FIG. 5. FIG. 5 shows that the electron lifetime of the semiconductor material including the PdSe.sub.2 thin film modified with the Pt nanoparticles of Second Embodiment was 77.9 picoseconds. In contrast, the electron lifetime of the semiconductor material including the PdSe.sub.2 thin film with no metal nanoparticles of Comparative Example 2 was 7.18 picoseconds. In the present embodiment as well, an increase in the electron lifetime by the modification with the Pt nanoparticles was confirmed.

[0108] Third Embodiment: In the present embodiment, a thin film of PtSe.sub.2 as a transition metal dichalcogenide thin film was formed on a base material, and the surface of the thin film was modified with Ru particles as metal nanoparticles, thereby producing a semiconductor material. Regarding the semiconductor material, the photoresponsivity to near-infrared rays was evaluated and the surface morphology was studied.

[Manufacturing of Semiconductor Material]

[0109] Formation of Transition Metal Dichalcogenide Thin Film

[0110] A SiO.sub.2 glass substrate was used as a base material as in First Embodiment, and a PtSe.sub.2 thin film was formed by a CVD method in the same manner as in First Embodiment. A platinum complex (DDAP) was used as a thin film raw material. The platinum complex was heated to be vaporized, and introduced together with a carrier gas into the reactor. The platinum complex vaporized was decomposed on the substrate, and platinum and selenium were reacted with each other to precipitate PtSe.sub.2, thereby forming a thin film. The conditions for film formation were the same as those in First Embodiment, and the film thickness of the PtSe.sub.2 thin film was 4 nm.

Modification Step with Metal Nanoparticles

[0111] The surface of the PtSe.sub.2 thin film formed above was modified with Ru nanoparticles by an atomic layer deposition method. The device used was the same as the CVD device used to form the PtSe.sub.2 thin film was used. As a Ru complex as a precursor (raw material gas) of the Ru nanoparticles, tricarbonyl(trimethylenemethane) ruthenium (Ru(TMM)(CO).sub.3) was used. The substrate on which the PtSe.sub.2 thin film had been formed was placed in a reactor, and the reactor was purged with argon (100 sccm). Then, the following (1) to (4) was regarded as one cycle. [0112] (1) Introduction of raw material gas [0113] Heating temperature of raw material: 10 C. [0114] Carrier gas: Argon/50 sccm [0115] Introduction time: 10 seconds [0116] (2) Exhaustion of raw material gas [0117] Purged with argon gas (100 sccm) [0118] Introduction time: 10 seconds [0119] (3) Introduction of reaction gas [0120] Reaction gas: Pure oxygen/50 sccm [0121] Introduction time: 10 seconds [0122] (4) Exhaustion of reaction gas [0123] Purged with argon gas (100 sccm) [0124] Introduction time: 10 seconds

[0125] In the present embodiment, 50 cycles each consisting of (1) to (4) above were performed to thereby modify the surface of the PtSe.sub.2 thin film with the Ru nanoparticles to manufacture a semiconductor material.

[Measurement of Average Particle Diameter and Percentage of Area of Metal Nanoparticles]

[0126] For the Ru nanoparticles on the surface of the semiconductor material of Third Embodiment, the average particle diameter and the percentage of the area were measured. The measurement of the average particle diameter and the percentage of the area of the Ru nanoparticles was based on surface observation with SEM in the same manner as in First Embodiment. The average particle diameter of the Ru nanoparticles was 12.47 nm. The percentage of the area of the Ru nanoparticles of the present embodiment was 1.98%. FIG. 6 shows an example of a SEM image of the semiconductor material (Ru/PtSe.sub.2) manufactured in Third Embodiment. [Evaluation of Photoresponsivity of Semiconductor Material]

[0127] On the semiconductor material of Third Embodiment produced above, the photoresponsivity to near-infrared rays was measured. As for the measurement method and the method for electrode formation were the same as in First Embodiment, and the wavelengths of the near-infrared rays used for irradiation were 740 nm, 850 nm and 940 nm. These measurement results are shown in FIG. 7. FIG. 7 shows the results of the semiconductor material (Ru/PtSe.sub.2) of the present embodiment and the semiconductor material without modification with Ru particles (bare PtSe.sub.2 thin film: Comparative Example 1).

[0128] From the measurement results of FIG. 7, it is found that the semiconductor material including the PtSe.sub.2 thin film modified with the Ru nanoparticles (Third Embodiment) was capable of generating a higher photocurrent than the semiconductor material including only the PtSe.sub.2 thin film (Comparative Example 1) in all wavelength ranges. In the present embodiment, it was possible to generate photocurrents approximately eight times larger. From the above-described results, it was confirmed that the light-receiving sensitivity of the transition metal dichalcogenide thin film was also improved by modification with the Ru nanoparticles.

INDUSTRIAL APPLICABILITY

[0129] As described above, the semiconductor material of the invention and the method for producing the same satisfy all requirements, specifically, a high light-receiving sensitivity, a low production cost and use at room temperature, and the semiconductor material is useful as light-receiving elements. Particularly, since the light-receiving sensitivity in the near-infrared range is extremely superior to those of conventional transition metal dichalcogenides, the semiconductor material of the present invention can be expected to contribute to additional improvement in measurement accuracy as a material for light-receiving elements in LIDAR applications.