A method for fabricating a high-performance infrared photodetector with an NN-type two-dimensional heterojunction

Abstract

This application relates to the field of infrared detector technology, specifically disclosing a method for fabricating a high-performance infrared photodetector with an NN-type two-dimensional heterojunction. The method includes the following steps: S1, substrate preparation: a Si / SiO2 substrate is cut, cleaned, and dried for later use; S2, heterojunction structure construction: a few-layer MoWS4 thin film is transferred to the substrate obtained in S1 using a mechanical lift-off method, and then a MoWSe4 thin film is stacked and transferred onto the MoWS4 thin film to form a MoWSe4 / MoWS4 heterojunction; S3, electrode fabrication: a PMMA photoresist layer is coated on the surface of the heterojunction, and electrode patterns are fabricated, followed by metal electrode evaporation, electrode lift-off, and cleaning; S4, annealing treatment; S5, material and device characterization. The infrared photodetector of this application can be used in near-infrared light detection, infrared imaging, and photoelectric sensing, and has the advantages of high detectivity, fast response speed, and no need for complex cryogenic cooling.

Description

Technical Field

[0001] This application relates to the field of infrared detector technology, and more specifically, to a method for fabricating a high-performance infrared photodetector with an NN-type two-dimensional heterojunction. Background Technology

[0002] In the modern information society, photodetectors play an indispensable role as key components in the field of optoelectronics. They can efficiently convert optical signals into electrical signals and are widely used in many fields such as optical communication, imaging sensing, aerospace remote sensing, energy, and medicine. With the rapid development of technologies such as communication, artificial intelligence, and autonomous driving, more stringent requirements have been placed on the performance of photodetectors, such as electrical response, detectivity and response speed, integration density, and power efficiency.

[0003] Most photodetectors rely on semiconductor materials such as silicon and indium gallium arsenide, but these materials face significant bottlenecks when developing towards miniaturization and high performance: dimensional limitations make it difficult to optimize carrier transport, limiting the improvement of response speed; size reduction easily leads to a weakening of quantum confinement effect and an increase in leakage current, reducing detection sensitivity and stability; and the fixed band structure makes it difficult to flexibly control the light absorption range and carrier separation efficiency, restricting the application of wide-spectrum detection, resulting in low light absorption and carrier separation efficiency of detectors over a wide spectral range, limited response speed, and insufficient detection sensitivity. Summary of the Invention

[0004] To address the problem that photodetectors often rely on bulk semiconductor materials such as silicon and indium gallium arsenide, resulting in low light absorption and carrier separation efficiency and limited response speed over a wide spectral range, this application provides a method for fabricating a high-performance infrared photodetector with an NN-type two-dimensional heterojunction.

[0005] This application provides a method for fabricating a high-performance infrared photodetector with an NN-type two-dimensional heterojunction, employing the following technical solution:

[0006] A method for fabricating a high-performance infrared photodetector with an NN-type two-dimensional heterojunction includes the following steps:

[0007] S1. Prepare the substrate: Cut and clean the Si / SiO2 substrate, and dry it for later use;

[0008] S2. Construction of heterojunction structure: The few-layer MoWS4 film is transferred to the substrate obtained in S1 by mechanical peeling, and then the MoWSe4 film is stacked and transferred onto the MoWS4 film to form a MoWSe4 / MoWS4 heterojunction.

[0009] S3. Electrode fabrication: A PMMA photoresist layer is coated on the surface of the MoWSe4 / MoWS4 heterojunction obtained in S2, and an electrode pattern is fabricated. Then, metal electrode evaporation is performed, followed by electrode stripping and cleaning to form a heterojunction device.

[0010] S4. Annealing treatment: The heterojunction device obtained in S3 is subjected to rapid annealing treatment to obtain the annealed workpiece.

[0011] S5. Material and Device Characterization: Perform material and device characterization measurements on the annealed workpiece obtained in S4 to complete the detector fabrication.

[0012] By adopting the above technical solution, the back-to-back stacked NN-type MoWSe4 / MoWS4 heterojunction is constructed by mechanical stripping and van der Waals integration. The type II band arrangement promotes the separation and directional transport of photogenerated holes and electrons under near-infrared light irradiation. Moreover, the preparation method itself has the advantages of being simple and low-cost. Therefore, an infrared detector with high detectivity, fast response speed and no need for cryogenic cooling is obtained, providing a way to solve the problems of high cost and large size of traditional infrared detectors.

[0013] Preferably, in step S1, the substrate is a Si / SiO2 substrate, and the Si / SiO2 substrate is cut into squares of 1-3 cm in size.

[0014] By adopting the above technical solution, the use of a 1 to 3 cm square Si / SiO2 substrate, which is easy to hold and fix on the platform during subsequent micro-nano processing operations such as mechanical peeling, microscope positioning and photolithography, provides a stable and appropriately sized carrier for material transfer. Therefore, a substrate that is easy to operate and conducive to improving the yield of the process is obtained.

[0015] Preferably, in step S1, the cleaning process involves: sequentially immersing the cut substrate in an acetone solution for ultrasonic cleaning for 4-6 minutes, then immersing it in an isopropanol solution for ultrasonic cleaning for 4-6 minutes, followed by ultrasonic cleaning with deionized water for 4-6 minutes, rinsing with deionized water, and drying with a nitrogen gun; the drying process involves placing the cleaned substrate on a heating table to remove moisture.

[0016] By adopting the above technical solution, the substrate surface is cleaned in a stepwise ultrasonic cleaning process using acetone, isopropanol, and deionized water. Acetone dissolves and removes organic contaminants and grease from the substrate surface, isopropanol serves as an intermediate solvent to remove acetone residue and further clean the surface, and subsequent deionized water cleaning thoroughly removes polar residues and particulate contaminants. Finally, nitrogen gas is used to dry the surface and heating is applied to eliminate water droplets and moisture. Therefore, an ultra-clean substrate surface free of organic and inorganic residues is obtained, providing a clean interface for subsequent dry transfer of two-dimensional materials and avoiding the impact of contaminants on the heterojunction interface quality and device performance.

[0017] Preferably, the ultrasonic cleaning time is 5 to 10 minutes; the heating temperature is 100 to 200°C.

[0018] By adopting the above technical solution, the time for each ultrasonic cleaning step is extended and set to 5 to 10 minutes, ensuring sufficient contact and reaction time between the solvent and contaminants. At the same time, the temperature of the heating stage is set to 100 to 200 degrees Celsius. This temperature range can promote the desorption of water molecules adsorbed on the substrate surface without causing thermal damage to the substrate structure. Therefore, a more thorough and reliable substrate surface cleaning and drying effect is obtained, laying the foundation for the preparation of high-quality heterojunctions.

[0019] Preferably, in step S2, the mechanical peeling method and the transfer process are both carried out in a nitrogen glove box. The mechanical peeling method specifically involves: tearing out MoWS4 films of different thicknesses with blue film tape, cutting the PDMS film into rectangles, pasting them on the surface of a glass slide, then transferring the MoWS4 material on the blue film tape to the PDMS, and under a microscope, finding a MoWS4 film of suitable thickness and size and positioning it for transfer to the prepared Si / SiO2 substrate.

[0020] By adopting the above technical solution, since the entire material peeling and transfer process is completed in a glove box filled with inert gas, the environment isolates oxygen and water vapor in the air, thereby preventing the surface oxidation or adsorption of water molecules of the two-dimensional material MoWS4 during the transfer process; using blue film tape for mechanical peeling to obtain a few-layer film, and using PDMS film as an elastic transfer medium to facilitate precise picking and placement under a microscope, a few-layer MoWS4 film with a clean interface and no oxide layer contamination is obtained, and it is successfully positioned and transferred to the target substrate, ensuring the intrinsic quality of the material as the contact layer and the integrity of the subsequent heterojunction interface.

[0021] Preferably, in step S2, the specific method for transferring the MoWSe4 film onto the MoWS4 film is as follows: the MoWSe4 film is obtained by mechanical peeling, and the position is accurately located under a microscope, and the MoWSe4 film is transferred onto the MoWS4 film to form a MoWSe4 / MoWS4 heterojunction.

[0022] By adopting the above technical solution, since the same mechanical exfoliation method is used to obtain a few-layer MoWSe4 film, and with the assistance of an optical microscope, the MoWSe4 film is precisely aligned and stacked on the pre-transferred MoWS4 film. This operation relies on van der Waals forces to bond the two layers together. Therefore, a vertically stacked MoWSe4 / MoWS4 van der Waals heterojunction is successfully constructed, in which the MoWSe4 layer serves as the light absorption layer and the MoWS4 layer serves as the contact layer, laying the foundation for the formation of type II band alignment.

[0023] Preferably, in step S3, the electrode pattern is fabricated by etching a preset electrode pattern onto a photoresist layer using electron beam exposure, and then placing it in a corresponding developing solution for development after exposure; the metal electrode is deposited by first depositing a 4-6 nm thick Cr transition layer, and then depositing a 55-65 nm thick Au conductive layer.

[0024] By adopting the above technical solution, the method achieves micro- and nano-scale patterning by defining electrode patterns using high-precision electron beam lithography, meeting the processing requirements of micro-electrodes for two-dimensional devices. When evaporating metal electrodes, a 4 to 6 nanometer-thick chromium layer is first deposited. The chromium layer can form chemical bonds with the substrate and two-dimensional materials, enhancing the adhesion and stability of the electrode. Subsequently, a 55 to 65 nanometer-thick gold layer is deposited. Gold has conductivity and chemical stability and can serve as the main conductive channel. Therefore, source and drain electrodes with precise patterns, strong adhesion, and good conductivity are obtained, forming ohmic contacts with the two-dimensional materials, ensuring the effective injection and extraction of electrical signals.

[0025] Preferably, in step S3, the electrode stripping and cleaning are performed as follows: after the metal electrode is vapor-deposited, the sample is placed in an acetone solution for electrode stripping, during which air is gently blown through with a pipette; after stripping, the sample is rinsed with isopropanol and deionized water in sequence, and finally dried with a nitrogen gun to obtain a heterojunction device.

[0026] By adopting the above technical solution, after metal evaporation, acetone solution is used for stripping. Acetone dissolves the PMMA photoresist, which serves as a sacrificial layer, allowing the excess metal layer covering the photoresist to detach from the sample, while the metal directly attached to the heterojunction through the pattern window is retained. Gently blowing air with a pipette helps to agitate the liquid, promoting the detachment of unattached metal without damaging the delicate electrodes. Subsequent rinsing with isopropanol and deionized water can gradually remove acetone residue and other contaminants. Therefore, a complete electrode structure with clear outlines and no metal residue short circuits is obtained, completing the fabrication of the heterojunction device.

[0027] Preferably, in step S4, the rapid annealing is carried out under a nitrogen protective atmosphere, the annealing temperature is 150-250°C, and the annealing time is 1-3 minutes; after annealing, the furnace is cooled to room temperature.

[0028] By adopting the above technical solution, the device is subjected to rapid thermal annealing at 150 to 250 degrees Celsius for 1 to 3 minutes under nitrogen protection. Nitrogen protection prevents the oxidation of electrodes and two-dimensional materials at high temperatures. The appropriate annealing temperature and time can promote the mutual diffusion between metal electrode atoms and surface atoms of two-dimensional materials, reduce interface defects, lower contact resistance, and release some of the stress generated during processing. Therefore, a heterojunction device with better ohmic contact characteristics, stable electrical performance, and high overall reliability is obtained.

[0029] Preferably, in step S5, the thickness of MoWSe4 and MoWS4 materials is measured using an atomic force microscope, and the layer information and interlayer spacing of MoWSe4 and MoWS4 materials, as well as the generation and contamination of amorphous oxides during the fabrication of the heterojunction are measured using a transmission electron microscope.

[0030] By adopting the above technical solution, the thickness of the transferred MoWSe4 and MoWS4 films is measured using atomic force microscopy, directly characterizing the number of layers in the materials and ensuring that they are few-layer structures that meet the design requirements. The high-resolution imaging and diffraction capabilities of transmission electron microscopy are used to analyze the layered stacking structure of the heterojunction, measure the interlayer spacing, and detect the presence of amorphous oxides or other process-introduced contaminants at the interface. Therefore, quantitative and qualitative characterization results of the heterojunction material thickness, crystal structure quality, and interface cleanliness are obtained, providing structural evidence for verifying the success of the device fabrication process and subsequent performance analysis.

[0031] In summary, this application has the following beneficial effects:

[0032] 1. This application employs a back-to-back stacked NN-type MoWSe4 / MoWS4 heterojunction, which forms a type II band arrangement. When N-type MoWSe4 contacts N-type MoWS4, there is a Fermi level difference, which causes electrons to migrate from the high Fermi level MoWSe4 layer to the low Fermi level MoWS4 layer, while holes migrate in the opposite direction. Under near-infrared light irradiation, photogenerated electron-hole pairs can be efficiently separated and directionally transported under the drive of the built-in electric field, thereby forming a photocurrent. Therefore, high-performance infrared detection with high detectivity, fast response speed and no need for complex cryogenic cooling is obtained.

[0033] 2. In this application, a preferred electrode preparation method is to deposit chromium and gold metal layers in steps and then perform rapid annealing. The chromium layer can form strong chemical bonds with the two-dimensional material and the substrate surface, providing a highly adherent substrate, while the gold layer constructs a highly conductive channel on it. The subsequent rapid annealing under nitrogen protection promotes the interdiffusion of chromium and gold atoms with sulfur and selenium atoms on the surface of the two-dimensional material. This process reduces the defect state density at the metal-semiconductor interface, enabling the formation of a high-quality ohmic contact between the metal electrode and the NN-type heterojunction. Therefore, it achieves the effects of low contact resistance, stable electrical performance, and efficient collection of photogenerated carriers.

[0034] 3. The method of this application employs ultra-clean substrate treatment, precise stacking of heterojunctions in an inert atmosphere, patterned fabrication of metal electrodes, and rapid annealing process. The ultra-clean substrate provides a contamination-free substrate for material transfer; the stacking in an inert environment ensures interface quality; and the Cr / Au electrode forms an ohmic contact with the material. The final rapid annealing further reduces the contact resistance and releases process stress, thus obtaining an infrared photodetector with stable process, good repeatability, and excellent overall performance. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of a high-performance infrared photodetector of NN-type two-dimensional heterojunction proposed in this application;

[0036] Figure 2 This is a flowchart illustrating a method for fabricating a high-performance infrared photodetector of an NN-type two-dimensional heterojunction proposed in this application.

[0037] Figure 3 Raman spectra of MoWSe4, MoWS4 materials, and MoWSe4 / MoWS4 heterojunction. Detailed Implementation

[0038] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0039] Technical concept:

[0040] Most photodetectors rely on semiconductor materials such as silicon and indium gallium arsenide, but these materials face significant bottlenecks when developing towards miniaturization and high performance: dimensional limitations make it difficult to optimize carrier transport, limiting the improvement of response speed; size reduction easily leads to a weakening of quantum confinement effect and an increase in leakage current, reducing detection sensitivity and stability; and the fixed band structure makes it difficult to flexibly control the light absorption range and carrier separation efficiency, restricting the application of wide-spectrum detection, resulting in low light absorption and carrier separation efficiency of detectors over a wide spectral range, limited response speed, and insufficient detection sensitivity.

[0041] This application discloses a method for fabricating a high-performance infrared photodetector with an NN-type two-dimensional heterojunction. The method includes the following steps: S1, substrate preparation: a Si / SiO2 substrate is cut, cleaned, and dried for later use; S2, heterojunction structure construction: a few-layer MoWS4 thin film is transferred to the substrate obtained in S1 using a mechanical lift-off method, and then a MoWSe4 thin film is stacked and transferred onto the MoWS4 thin film to form a MoWSe4 / MoWS4 heterojunction; S3, electrode fabrication: a PMMA photoresist layer is coated on the surface of the heterojunction, and electrode patterns are fabricated, followed by metal electrode evaporation, electrode lift-off, and cleaning; S4, annealing treatment; S5, material and device characterization.

[0042] This application employs a back-to-back stacked NN-type MoWSe4 / MoWS4 heterojunction, which forms a type II band arrangement. When N-type MoWSe4 contacts N-type MoWS4, there is a Fermi level difference, which causes electrons to migrate from the high Fermi level MoWSe4 layer to the low Fermi level MoWS4 layer, while holes migrate in the opposite direction. Under near-infrared light irradiation, photogenerated electron-hole pairs can be efficiently separated and directionally transported under the drive of the built-in electric field, thereby forming a photocurrent. Therefore, high-performance infrared detection with high detectivity, fast response speed and no need for complex cryogenic cooling is obtained.

[0043] Example 1: This example provides a method for fabricating a high-performance infrared photodetector with an NN-type two-dimensional heterojunction, comprising the following steps:

[0044] S1: Prepare the substrate: Cut and clean the Si / SiO2 substrate, and dry it for later use.

[0045] The substrate is a Si / SiO2 substrate, which is cut into 1cm squares. The cleaning process is as follows: the cut substrate is ultrasonically cleaned in acetone solution for 5 minutes, then ultrasonically cleaned in isopropanol solution for 5 minutes, then ultrasonically cleaned in deionized water for 5 minutes, then rinsed with deionized water, and then dried with a nitrogen gun. The drying process is to place the cleaned substrate on a heating table to remove moisture at a temperature of 100°C.

[0046] S2: Heterojunction structure construction: The few-layer MoWS4 film is transferred to the substrate obtained in S1 by mechanical peeling, and then the MoWSe4 film is stacked and transferred onto the MoWS4 film to form a MoWSe4 / MoWS4 heterojunction.

[0047] The mechanical exfoliation method and the transfer process were both carried out in a nitrogen glove box. The mechanical exfoliation method was as follows: MoWS4 films of different thicknesses were torn off with blue film tape, the PDMS film was cut into rectangles and pasted on the surface of a glass slide, and then the MoWS4 material on the blue film tape was transferred to the PDMS. Under a microscope, a MoWS4 film of appropriate thickness and size was located and transferred to the prepared Si / SiO2 substrate. The specific method for transferring the MoWSe4 film onto the MoWS4 film was as follows: the MoWSe4 film was obtained by mechanical exfoliation, and the position was accurately located under a microscope. The MoWSe4 film was then transferred onto the MoWS4 film to form a MoWSe4 / MoWS4 heterojunction.

[0048] S3: Electrode fabrication: A PMMA photoresist layer is coated on the surface of the MoWSe4 / MoWS4 heterojunction obtained in S2, and an electrode pattern is fabricated. Then, metal electrode evaporation is performed, followed by electrode stripping and cleaning to form a heterojunction device.

[0049] The electrode pattern fabrication process involves etching a pre-defined electrode pattern onto a photoresist layer using electron beam exposure, followed by development in a corresponding developer solution. The metal electrode deposition process involves first depositing a 4nm thick Cr transition layer, followed by depositing a 55nm thick Au conductive layer. The electrode stripping and cleaning process involves immersing the sample in an acetone solution after metal electrode deposition, gently blowing air through the sample with a pipette during the process. After stripping, the sample is rinsed sequentially with isopropanol and deionized water, and finally dried with a nitrogen gun to obtain a heterojunction device.

[0050] S4: Annealing treatment: The heterojunction device obtained in S3 is subjected to rapid annealing treatment to obtain the annealed workpiece.

[0051] The rapid annealing process was carried out under a nitrogen protective atmosphere at a temperature of 150°C for 1 minute; after annealing, the furnace was cooled to room temperature.

[0052] S5: Material and Device Characterization: Perform material and device characterization measurements on the annealed workpiece obtained in S4 to complete the detector fabrication.

[0053] Among them, atomic force microscopy was used to measure the thickness of MoWSe4 and MoWS4 materials, and transmission electron microscopy was used to measure the layer information and interlayer spacing of MoWSe4 and MoWS4 materials, as well as the generation and contamination of amorphous oxides during the fabrication of heterojunctions.

[0054] Example 2: This example provides a method for fabricating a high-performance infrared photodetector with an NN-type two-dimensional heterojunction, comprising the following steps:

[0055] S1: Prepare the substrate: Cut and clean the Si / SiO2 substrate, and dry it for later use.

[0056] The substrate is a Si / SiO2 substrate, which is cut into 2cm squares. The cleaning process is as follows: the cut substrate is ultrasonically cleaned in acetone solution for 7.5 min, then ultrasonically cleaned in isopropanol solution for 7.5 min, then ultrasonically cleaned in deionized water for 7.5 min, then rinsed with deionized water and dried with a nitrogen gun. The drying process is to place the cleaned substrate on a heating table to remove moisture at a temperature of 150°C.

[0057] S2: Heterojunction structure construction: The few-layer MoWS4 film is transferred to the substrate obtained in S1 by mechanical peeling, and then the MoWSe4 film is stacked and transferred onto the MoWS4 film to form a MoWSe4 / MoWS4 heterojunction.

[0058] The mechanical exfoliation method and the transfer process were both carried out in a nitrogen glove box. The mechanical exfoliation method was as follows: MoWS4 films of different thicknesses were torn off with blue film tape, the PDMS film was cut into rectangles and pasted on the surface of a glass slide, and then the MoWS4 material on the blue film tape was transferred to the PDMS. Under a microscope, a MoWS4 film of appropriate thickness and size was located and transferred to the prepared Si / SiO2 substrate. The specific method for transferring the MoWSe4 film onto the MoWS4 film was as follows: the MoWSe4 film was obtained by mechanical exfoliation, and the position was accurately located under a microscope. The MoWSe4 film was then transferred onto the MoWS4 film to form a MoWSe4 / MoWS4 heterojunction.

[0059] S3: Electrode fabrication: A PMMA photoresist layer is coated on the surface of the MoWSe4 / MoWS4 heterojunction obtained in S2, and an electrode pattern is fabricated. Then, metal electrode evaporation is performed, followed by electrode stripping and cleaning to form a heterojunction device.

[0060] The electrode pattern fabrication process involves etching a pre-defined electrode pattern onto a photoresist layer using electron beam exposure, followed by development in a corresponding developer solution. The metal electrode deposition process involves first depositing a 5nm thick Cr transition layer, followed by depositing a 60nm thick Au conductive layer. The electrode stripping and cleaning process involves immersing the sample in an acetone solution after metal electrode deposition, gently blowing air through the sample with a pipette during the process. After stripping, the sample is rinsed sequentially with isopropanol and deionized water, and finally dried with a nitrogen gun to obtain a heterojunction device.

[0061] S4: Annealing treatment: The heterojunction device obtained in S3 is subjected to rapid annealing treatment to obtain the annealed workpiece.

[0062] The rapid annealing process was carried out under a nitrogen protective atmosphere at a temperature of 200°C for 2 minutes; after annealing, the furnace was cooled to room temperature.

[0063] S5: Material and Device Characterization: Perform material and device characterization measurements on the annealed workpiece obtained in S4 to complete the detector fabrication.

[0064] Among them, atomic force microscopy was used to measure the thickness of MoWSe4 and MoWS4 materials, and transmission electron microscopy was used to measure the layer information and interlayer spacing of MoWSe4 and MoWS4 materials, as well as the generation and contamination of amorphous oxides during the fabrication of heterojunctions.

[0065] Example 3: This example provides a method for fabricating a high-performance infrared photodetector with an NN-type two-dimensional heterojunction, comprising the following steps:

[0066] S1: Prepare the substrate: Cut and clean the Si / SiO2 substrate, and dry it for later use.

[0067] The substrate is a Si / SiO2 substrate, which is cut into 3cm squares. The cleaning process is as follows: the cut substrate is ultrasonically cleaned in acetone solution for 10 minutes, then ultrasonically cleaned in isopropanol solution for 10 minutes, then ultrasonically cleaned in deionized water for 10 minutes, then rinsed with deionized water, and then dried with a nitrogen gun. The drying process is to place the cleaned substrate on a heating table to remove moisture at a temperature of 200°C.

[0068] S2: Heterojunction structure construction: The few-layer MoWS4 film is transferred to the substrate obtained in S1 by mechanical peeling, and then the MoWSe4 film is stacked and transferred onto the MoWS4 film to form a MoWSe4 / MoWS4 heterojunction.

[0069] The mechanical exfoliation method and the transfer process were both carried out in a nitrogen glove box. The mechanical exfoliation method was as follows: MoWS4 films of different thicknesses were torn off with blue film tape, the PDMS film was cut into rectangles and pasted on the surface of a glass slide, and then the MoWS4 material on the blue film tape was transferred to the PDMS. Under a microscope, a MoWS4 film of appropriate thickness and size was located and transferred to the prepared Si / SiO2 substrate. The specific method for transferring the MoWSe4 film onto the MoWS4 film was as follows: the MoWSe4 film was obtained by mechanical exfoliation, and the position was accurately located under a microscope. The MoWSe4 film was then transferred onto the MoWS4 film to form a MoWSe4 / MoWS4 heterojunction.

[0070] S3: Electrode fabrication: A PMMA photoresist layer is coated on the surface of the MoWSe4 / MoWS4 heterojunction obtained in S2, and an electrode pattern is fabricated. Then, metal electrode evaporation is performed, followed by electrode stripping and cleaning to form a heterojunction device.

[0071] The electrode pattern fabrication process involves etching a pre-defined electrode pattern onto a photoresist layer using electron beam exposure, followed by development in a corresponding developer solution. The metal electrode deposition process involves first depositing a 6nm thick Cr transition layer, followed by depositing a 65nm thick Au conductive layer. The electrode stripping and cleaning process involves immersing the sample in an acetone solution after metal electrode deposition, gently blowing air through the sample with a pipette during the process. After stripping, the sample is rinsed sequentially with isopropanol and deionized water, and finally dried with a nitrogen gun to obtain a heterojunction device.

[0072] S4: Annealing treatment: The heterojunction device obtained in S3 is subjected to rapid annealing treatment to obtain the annealed workpiece.

[0073] The rapid annealing process was carried out under a nitrogen protective atmosphere at a temperature of 250°C for 3 minutes; after annealing, the furnace was cooled to room temperature.

[0074] S5: Material and Device Characterization: Perform material and device characterization measurements on the annealed workpiece obtained in S4 to complete the detector fabrication.

[0075] Among them, atomic force microscopy was used to measure the thickness of MoWSe4 and MoWS4 materials, and transmission electron microscopy was used to measure the layer information and interlayer spacing of MoWSe4 and MoWS4 materials, as well as the generation and contamination of amorphous oxides during the fabrication of heterojunctions.

[0076] The NN-type two-dimensional heterojunction high-performance infrared photodetector prepared according to the methods described in Examples 1-3 above has the following structure, working principle, characterization method and results:

[0077] Structure: The detector is a vertically stacked van der Waals heterojunction structure, which from bottom to top includes a Si / SiO2 substrate, a MoWS4 material layer as a contact layer, a MoWSe4 material layer as an absorption layer, and gold / chromium (Au / Cr) metal electrodes (source electrode and drain electrode) fabricated on the surface of the heterojunction, which together constitute the MoWSe4 / MoWS4 heterojunction device.

[0078] Working principle: Its mechanism is based on the back-to-back NN-type type II band arrangement; when N-type MoWSe4 comes into contact with N-type MoWS4, due to the difference in their Fermi levels, electrons migrate from the higher Fermi level MoWSe4 layer to the lower Fermi level MoWS4 layer, while holes migrate in the opposite direction, thus forming a built-in electric field at the interface; under near-infrared light irradiation, the absorption layer generates photogenerated electron-hole pairs. These charge carriers are efficiently separated and directionally transported under the drive of the built-in electric field, with electrons moving towards the MoWS4 layer and holes moving towards the MoWSe4 layer, forming a stable photocurrent. The optical signal can be detected through an external circuit.

[0079] Characterization methods: After fabrication, atomic force microscopy (AFM) was used to measure the film thickness of MoWSe4 and MoWS4 materials, and transmission electron microscopy (TEM) was used to observe the layered structure and interlayer spacing of the materials, as well as to assess the amorphous oxides and interface contamination generated during the heterojunction preparation process, in order to confirm the quality and interface characteristics of the heterojunction.

[0080] Results: Raman spectroscopy characterization showed that MoWS4 was at ~349 cm⁻¹ -1 ~377 cm -1 and 411 cm -1 The characteristic peaks at ~241 cm⁻¹ and MoWSe⁴ at ~241 cm⁻¹ -1The strong peaks at the positions of the two materials confirm the structural integrity of both materials. The Raman spectrum of the heterojunction also contains these characteristic peaks, and the peak positions are slightly perturbed due to van der Waals coupling. This proves that a type II van der Waals heterojunction with stable structure and no degradation of phase state in each layer has been successfully constructed, providing a material basis for the structure to effectively promote the separation of photogenerated carriers and achieve high-performance photoelectric response.

[0081] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for fabricating a high-performance infrared photodetector with an NN-type two-dimensional heterojunction, characterized in that, Includes the following steps: S1. Prepare the substrate: Cut and clean the Si / SiO2 substrate, and dry it for later use; S2. Construction of heterojunction structure: The few-layer MoWS4 film is transferred to the substrate obtained in S1 by mechanical peeling, and then the MoWSe4 film is stacked and transferred onto the MoWS4 film to form a MoWSe4 / MoWS4 heterojunction. S3. Electrode fabrication: A PMMA photoresist layer is coated on the surface of the MoWSe4 / MoWS4 heterojunction obtained in S2, and an electrode pattern is fabricated. Then, metal electrode evaporation is performed, followed by electrode stripping and cleaning to form a heterojunction device. S4. Annealing treatment: The heterojunction device obtained in S3 is subjected to rapid annealing treatment to obtain the annealed workpiece. S5. Material and Device Characterization: Perform material and device characterization measurements on the annealed workpiece obtained in S4 to complete the detector fabrication.

2. The method for fabricating a high-performance infrared photodetector of NN-type two-dimensional heterojunction according to claim 1, characterized in that, In step S1, the substrate is a Si / SiO2 substrate, and the Si / SiO2 substrate is cut into squares of 1-3 cm in size.

3. The method for fabricating a high-performance infrared photodetector of NN-type two-dimensional heterojunction according to claim 1, characterized in that, In step S1, the cleaning process involves: sequentially immersing the cut substrate in an acetone solution for ultrasonic cleaning for 4-6 minutes, then immersing it in an isopropanol solution for ultrasonic cleaning for 4-6 minutes, followed by ultrasonic cleaning with deionized water for 4-6 minutes, rinsing with deionized water, and drying with a nitrogen gun; the drying process involves placing the cleaned substrate on a heating table to remove moisture.

4. The method for fabricating a high-performance infrared photodetector of NN-type two-dimensional heterojunction according to claim 3, characterized in that, The ultrasonic cleaning time is 5 to 10 minutes; the heating temperature is 100 to 200°C.

5. The method for fabricating a high-performance infrared photodetector of NN-type two-dimensional heterojunction according to claim 1, characterized in that, In step S2, both the mechanical peeling method and the transfer process are carried out in a nitrogen glove box. The mechanical peeling method is as follows: MoWS4 films of different thicknesses are peeled off with blue film tape, the PDMS film is cut into rectangles and pasted on the surface of the glass slide, and then the MoWS4 material on the blue film tape is transferred to the PDMS. Under the microscope, a MoWS4 film of appropriate thickness and size is located and transferred to the prepared Si / SiO2 substrate.

6. The method for fabricating a high-performance infrared photodetector of NN-type two-dimensional heterojunction according to claim 1, characterized in that, In step S2, the specific method for transferring the MoWSe4 film onto the MoWS4 film is as follows: the MoWSe4 film is obtained by mechanical peeling, and the position is accurately located under a microscope. The MoWSe4 film is then transferred onto the MoWS4 film to form a MoWSe4 / MoWS4 heterojunction.

7. The method for fabricating a high-performance infrared photodetector of an NN-type two-dimensional heterojunction according to claim 1, characterized in that, In step S3, the electrode pattern is fabricated by etching a preset electrode pattern onto a photoresist layer using electron beam exposure, and then placing it in a corresponding developing solution for development after exposure; the metal electrode is deposited by first depositing a 4-6 nm thick Cr transition layer, and then depositing a 55-65 nm thick Au conductive layer.

8. The method for fabricating a high-performance infrared photodetector of an NN-type two-dimensional heterojunction according to claim 1, characterized in that, In step S3, the electrode stripping and cleaning are performed as follows: after the metal electrode is vapor-deposited, the sample is placed in an acetone solution for electrode stripping, during which air is gently blown through with a pipette; after stripping, the sample is rinsed with isopropanol and deionized water in sequence, and finally dried with a nitrogen gun to obtain a heterojunction device.

9. The method for fabricating a high-performance infrared photodetector of NN-type two-dimensional heterojunction according to claim 8, characterized in that, In step S4, the rapid annealing process is carried out under a nitrogen protective atmosphere, with an annealing temperature of 150–250°C and an annealing time of 1–3 minutes; after annealing, the furnace is cooled to room temperature.

10. The method for fabricating a high-performance infrared photodetector of an NN-type two-dimensional heterojunction according to claim 1, characterized in that, In step S5, the thickness of MoWSe4 and MoWS4 materials is measured using atomic force microscopy, and the layer information and interlayer spacing of MoWSe4 and MoWS4 materials are measured using transmission electron microscopy, as well as the generation and contamination of amorphous oxides during the fabrication of the heterojunction.

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