Method for manufacturing photoelectric element

Abstract

To manufacture a photoelectric element made of a layered material having desired polarization characteristics stably with good reproducibility.SOLUTION: In a first step S101, reducing molecules are chemically adsorbed onto the surface of a semiconductor substrate to form an oxide film on the surface of the semiconductor substrate (adsorption step), in a second step S102, the oxide film is removed from the surface of the semiconductor substrate by etching using an etching solution that selectively dissolves the oxide film relative to the semiconductor substrate (removal step), and in a third step S103, a layered material is transferred onto the surface of the semiconductor substrate from which the oxide film has been removed (transfer step).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for fabricating a photoelectric device. [Background technology]

[0002] Layered materials are layered materials with thicknesses of only one or a few atoms. Transition metal dichalcogenides, a representative example, exhibit the properties of direct transition semiconductors when they are several atomic layers thick. The term "transition metal dichalcogenide" is a general term for compounds composed of transition metal atoms and chalcogen atoms. The energy band of transition metal dichalcogenides has two stable energy states in wavenumber space, known as the K point and the K' point. At the K point, transition metal dichalcogenides selectively interact with only right-handed circularly polarized light, while at the K' point, they selectively interact with only left-handed circularly polarized light. This characteristic polarization dependence has led to promising applications in optical elements, such as circularly polarized lasers (Non-Patent Document 1).

[0003] Another characteristic of transition metal dichalcogenides is that the way polarization occurs varies greatly depending on the type of exciton complex that contributes to the emission (neutral exciton, negatively charged exciton, positively charged exciton, etc.). For example, it has been reported that in the case of neutral excitons, any polarization state of the excitation light is maintained in the polarization state of the photoluminescence, whereas in the case of charged excitons, the circular polarization component of the excitation light is maintained but the linear polarization component is not (Non-Patent Document 2). Therefore, in order to achieve the desired polarization characteristics, it is necessary to precisely control the type of exciton complex that contributes to the emission.

[0004] Another important point in using layered materials is that they must be supported by a substrate to ensure the mechanical stability of thin films of a few atomic layers. The distance between the layered material and the substrate material is generally about 0.1 nm, and the layered material is held to the substrate by van der Waals forces. Because the layered material and the substrate are in such close contact, the surface condition of the substrate material has a significant impact on the optical properties of the layered material.

[0005] The surface condition of the substrate also changes the type of exciton complex formed within the layered material, which significantly affects the polarization characteristics. One known method for controlling the type of exciton complex is to use an electric field, but this is also strongly influenced by the surface of the substrate material, making it difficult to obtain stable, reproducible polarization characteristics. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] J. Pu et al., "Room-Temperature Chiral Light-Emitting Diode Based on Strained Monolayer Semiconductors", Advanced Materials, vol. 33, no. 36, 2100601, 2021. [Non-patent document 2] AM Jones et al., "Optical generation of excitonic valley coherence in monolayer WSe2", Nature Nanotechnology, vol. 8, pp. 634-638, 2013. Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, in photoelectric elements that utilize the light absorption and emission phenomenon that depends on the polarization of layered materials, the light absorption and emission characteristics of the layered material are strongly influenced by the surface of the substrate that supports the layered material, and therefore, there is a problem in that it is difficult to obtain the desired polarization characteristics stably and with good reproducibility.

[0008] The present invention has been made to solve the above problems, and has as its object to stably and reproducibly produce a photoelectric element made of a layer material having desired polarization characteristics. [Means for solving the problem]

[0009] The method for manufacturing a photoelectric element according to the present invention comprises an adsorption step of chemically adsorbing reducing molecules consisting of a compound of an element that is solid at room temperature onto the surface of a semiconductor substrate to form an oxide film consisting of an oxide of the element on the surface of the semiconductor substrate; a removal step of removing the oxide film from the surface of the semiconductor substrate by etching using an etching solution that selectively dissolves the oxide film on the semiconductor substrate; a transfer step of transferring a layered material onto the surface of the semiconductor substrate from which the oxide film has been removed; and a fourth step of manufacturing a photoelectric element composed of the layered material on the surface of the semiconductor substrate. [Effects of the Invention]

[0010] As described above, according to the present invention, reducing molecules made of compounds of elements that are solid at room temperature are chemically adsorbed onto the surface of a semiconductor substrate, and an oxide film made of an oxide of the element is formed on the surface of the semiconductor substrate. After this oxide film is removed, photoelectric elements made of layered materials with desired polarization characteristics can be produced stably and with good reproducibility. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a flowchart illustrating a method for manufacturing a photoelectric element according to an embodiment of the present invention. [Figure 2] FIG. 2 is a flowchart illustrating a method for manufacturing another photoelectric element according to an embodiment of the present invention. [Figure 3A]FIG. 3A is a photograph showing a transmission electron microscope image of the interface between a GaAs substrate and an aluminum oxide film formed on the surface of the GaAs substrate by the manufacturing method of the embodiment. [Figure 3B] FIG. 3B is a characteristic diagram showing a line profile by energy dispersive X-ray spectroscopy (EDX) in the interface region between the GaAs substrate and the aluminum oxide film formed by the manufacturing method of the embodiment. [Figure 4] FIG. 4 is a characteristic diagram showing the results of measuring the PL spectrum of the sample of the example. DETAILED DESCRIPTION OF THE INVENTION

[0012] A method for manufacturing a photoelectric element according to an embodiment of the present invention will be described below with reference to FIG.

[0013] First, in the first step S101, reducing molecules are chemically adsorbed onto the surface of the semiconductor substrate to form an oxide film on the surface of the semiconductor substrate (adsorption step). The molecules are compounds of elements that are solid at room temperature. The oxide film is an oxide of the element. For example, the element may be a metal, and the molecules may be an organometallic compound of a metal (Al), such as trimethylaluminum.

[0014] A native oxide film is formed on the surface of a semiconductor substrate, but by adsorbing the above-mentioned molecules in a high-temperature inert gas atmosphere, for example, the bonds between the atoms constituting the semiconductor substrate and oxygen atoms that made up the native oxide film are lost, and these oxygen atoms bond with the above-mentioned elements, and a new oxide film is formed from the oxide of this element.

[0015] Next, in a second step S102, the oxide film is removed from the surface of the semiconductor substrate by etching using an etching solution that selectively dissolves the oxide film on the semiconductor substrate (removal step). By removing the oxide film in this manner, it is possible to remove the native oxide film that was initially formed on the surface of the semiconductor substrate while suppressing the surface roughness of the semiconductor substrate.

[0016] Next, in a third step S103, the layered material is transferred onto the surface of the semiconductor substrate from which the oxide film has been removed (transfer step). Next, in a fourth step S104, a photoelectric element made of the layered material is fabricated on the surface of the semiconductor substrate (fourth step). In this way, a photoelectric element made of a semiconductor substrate and a layered material with a controlled surface state can be fabricated.

[0017] 2, after the second step S102 (removal step), the surface of the semiconductor substrate can be terminated (termination step) in the fifth step S105. By terminating the dangling bonds on the surface of the semiconductor substrate after removing the newly formed oxide film, it is possible to prevent oxygen atoms from bonding to form a new native oxide film. For example, the surface of the semiconductor substrate can be terminated with sulfur. In this case, the third step S103 (transfer step) of transferring the layered material to the surface of the semiconductor substrate is performed after the surface of the semiconductor substrate is terminated in the fifth step S105.

[0018] The following will explain in more detail using examples.

[0019] [Example] In the following, the layered material is a single layer of WS2, the semiconductor substrate is GaAs, and the reducing molecule is trimethylaluminum (TMA). In this case, the element that is solid at room temperature is Al.

[0020] First, in the adsorption process, TMA molecules are chemically adsorbed onto the surface of the semiconductor substrate at a temperature of 200°C. For example, the semiconductor substrate is loaded into a designated processing chamber, and the processing chamber is evacuated to reduce pressure. TMA gas is then supplied into the processing chamber for a processing time of 0.1 seconds, allowing the TMA molecules to chemically adsorb onto the surface of the semiconductor substrate. Next, high-purity nitrogen gas is introduced into the processing chamber and held for 3 seconds to purge unreacted TMA molecules and by-products generated during chemical adsorption. This process of introducing TMA gas and purging is repeated 60 times.

[0021] Figure 3A shows a transmission electron microscope (TEM) image of the interface between a GaAs substrate and an aluminum oxide film formed on the surface of the semiconductor substrate (GaAs substrate) by the above-mentioned process. Figure 3B shows a line profile of this interface region measured by energy dispersive X-ray spectroscopy (EDX). The line profile shown in Figure 3B shows the sum of the signals from Ga and As atoms. By adsorbing TMA molecules and forming an aluminum oxide film in this way, the surface of the GaAs substrate achieved a surface roughness of 1.1 nm.

[0022] Next, in the removal process, the aluminum oxide film formed on the surface of the GaAs substrate was removed by etching using a BOE solution consisting of hydrofluoric acid and ammonium fluoride as an etchant. In addition, in the termination process, the surface of the GaAs substrate was terminated with sulfur. For example, the surface of the GaAs substrate can be terminated with sulfur by heating a solution of thioacetamide powder in ammonia water to 78°C and immersing the GaAs substrate in this solution for 5 minutes.

[0023] Next, a single layer of WS2 was transferred onto a GaAs substrate that had been subjected to the removal process, resulting in Example Sample Type A. Similarly, a single layer of WS2 was transferred onto a GaAs substrate that had been subjected to the termination process, resulting in Example Sample Type B. Furthermore, a comparative sample Type C was fabricated by transferring a single layer of WS2 onto a GaAs substrate without performing the adsorption and removal processes according to the embodiment.

[0024] The PL spectrum measurement results for each sample are shown in Figure 4. Figure 4 also shows the PL spectrum of WS2 in a sample (silicon) in which a single layer of WS2 was transferred onto the surface of a Si substrate with a 300 nm thick silicon oxide (SiO2) layer. The sample (silicon) is shown to reveal the intrinsic photoelectric properties of the single layer of WS2.

[0025] In this PL measurement, the monolayer WS2 is excited by linearly polarized light, and the exciton coherence is identified by comparing the intensity of both the linearly polarized component of the excitation light and the orthogonal component of the exciton emission. In Type C, the two components have almost the same intensity, as in intrinsic WS2, but in Types A and B, significant intensity differences are observed between the two components.

[0026] This means that the carrier concentration of the monolayer WS2 decreased from Type C to Types A and B, suggesting that the removal of the native oxide film promoted the transfer of electrons from the monolayer WS2 to the GaAs substrate during the transfer of the monolayer WS2. Furthermore, the difference in intensity between the two components was nearly identical in Types A and B, suggesting that the carrier concentrations of the monolayer WS2 were nearly identical. However, Type A exhibited a spectral shoulder near 1.95 eV, suggesting the occurrence of exciton localization. However, this shoulder disappeared in Type B. It is believed that the sulfur-termination of the GaAs substrate resolved the exciton localization.

[0027] Here, semiconductor materials are promising as materials for the support substrate that supports the layered material, as they allow for conventional processes and control of electrical properties. The structures that have been proposed to place layered materials on a semiconductor substrate can be classified into the following three types: (1) (2) and (3).

[0028] (1) A structure created by degreasing a semiconductor substrate and then transferring layered materials onto it. (2) A structure created by directly etching the native oxide film on a semiconductor substrate and then transferring a layered material. (3) A structure created by epitaxially growing layered materials on a semiconductor substrate.

[0029] In (1), the semiconductor substrate is limited to a state where it is covered with a native oxide film. In (2), the surface roughness of the semiconductor substrate after etching often exceeds the film thickness of the layered material due to the presence of the native oxide film, which is often amorphous. Therefore, in (2), it is difficult to precisely control the properties of the layered material. In (3), the possibility of epitaxial growth is determined by the difference in crystal symmetry and lattice constant between the semiconductor substrate and the layered material, as well as the surface condition of the semiconductor substrate, which restricts the semiconductor substrate and its surface condition, as well as the layered material that can be epitaxially grown.

[0030] To address these issues, the above-described embodiment makes it possible to control the surface condition of the substrate on which the layered material is disposed so as to obtain the desired polarization characteristics, thereby enabling stable operation with good reproducibility. Furthermore, high-quality surfaces can be achieved for a wide range of semiconductor substrates, not just the GaAs substrate shown in the examples. Furthermore, since the semiconductor substrate and the layered material are bonded by van der Waals forces and epitaxial growth is not used, there are no restrictions on the combination of the semiconductor substrate and the layered material, the twist angle, or the surface condition of the semiconductor substrate. This solves the problems of the prior art and enables the realization of photoelectric elements with an extremely high degree of freedom.

[0031] As described above, according to the embodiment of the present invention, reducing molecules made of compounds of elements that are solid at room temperature are chemically adsorbed onto the surface of a semiconductor substrate, and an oxide film made of an oxide of the element is formed on the surface of the semiconductor substrate. After this, the oxide film is removed, so that photoelectric elements made of layered materials with desired polarization characteristics can be produced stably and with good reproducibility.

[0032] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention.

Claims

1. an adsorption step of chemically adsorbing reducing molecules made of a compound of an element that is solid at room temperature onto a surface of a semiconductor substrate to form an oxide film made of an oxide of the element on the surface of the semiconductor substrate; a removing step of removing the oxide film from the surface of the semiconductor substrate by etching using an etching solution that selectively dissolves the oxide film on the semiconductor substrate; a transfer step of transferring a layered material onto the surface of the semiconductor substrate from which the oxide film has been removed; a fourth step of fabricating a photoelectric element made of the layered material on the surface of the semiconductor substrate; A method for manufacturing a photoelectric element comprising:

2. 2. The method for manufacturing a photoelectric element according to claim 1, a termination step of terminating the surface of the semiconductor substrate after the removing step; The transfer step is a method for producing a photoelectric element, in which the layered material is transferred onto the surface of the semiconductor substrate after the surface of the semiconductor substrate is terminated.

3. 3. The method for manufacturing a photoelectric element according to claim 2, The termination step is a method for manufacturing a photoelectric element in which the surface of the semiconductor substrate is terminated with sulfur.

4. The method for producing a photoelectric element according to any one of claims 1 to 3, A method for producing a photoelectric element, wherein the element is a metal and the molecule is an organometallic compound of the metal.

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