Sandwich type Van der Waals heterojunction photoelectric detector and preparation method thereof

Abstract

The invention discloses a sandwich type Van der Waals heterojunction photoelectric detector and a preparation method thereof, and belongs to the technical field of optoelectronic devices. The detector comprises a sandwich-type heterojunction formed by a p-type rare earth co-doped tungsten disulfide layer, a graphene intermediate layer and a p-type narrow-band-gap molybdenum ditelluride layer which are stacked in sequence. Wherein rare earth doping is used for passivating defects and widening a spectrum; the graphene is used as an ultrafast carrier transport channel and an interface passivation layer; molybdenum ditelluride is used to extend infrared response and provide good ohmic contact. According to the preparation method, doped tungsten disulfide is synthesized through chemical vapor deposition, graphene and molybdenum ditelluride are accurately stacked in combination with a microcell fixed-point dry transfer technology, and finally the electrode is prepared through photoetching. The device shows extremely high responsivity, detection rate and external quantum efficiency in visible light and near-infrared bands, solves the problems of multiple interface defects, low carrier mobility and narrow spectral range of a traditional photoelectric detector, and provides a new scheme for high-performance broadband photoelectric detection.

Description

Technical Field

[0001] This invention relates to a sandwich-type van der Waals heterojunction photodetector and its fabrication method, belonging to the field of two-dimensional materials and optoelectronic devices technology, and is particularly applicable to sandwich-type van der Waals heterojunction photodetectors and their fabrication. Background Technology

[0002] With the rapid development of fields such as optical communication, environmental monitoring, and biomedical imaging, the demand for photodetectors (PDs) that combine broadband response, ultra-high sensitivity, and fast response speed is becoming increasingly urgent. Two-dimensional van der Waals heterojunctions (vdWHs), due to their interlayer bonding solely through van der Waals forces, overcome the stringent lattice matching requirements of traditional semiconductor heterojunctions, becoming an ideal platform for constructing next-generation high-performance optoelectronic devices. Their atomically flat interfaces and flexibly designable band structures offer enormous potential for efficiently separating photogenerated carriers and modulating photoelectric performance.

[0003] At present, some progress has been made in the research of van der Waals heterojunction photodetectors based on bilayer two-dimensional materials, but there are still significant technical bottlenecks: First, intrinsic defects (such as sulfur vacancies and metal vacancies) and interlayer interface defects in two-dimensional materials can induce nonradiative recombination of photogenerated carriers, which seriously restricts the improvement of device responsivity and external quantum efficiency. For example, although the GeSe / WS2 vertical heterojunction exhibits a certain photoelectric response, the interface defects lead to poor carrier separation efficiency (see reference [1]). Second, the carrier mobility of two-dimensional materials is limited, which restricts the extraction efficiency and response speed of photocurrent. For example, although the PdSe2 / NbSe2 heterojunction achieves an ultrafast response (~1.6 / 1.9 µs), its responsivity is only 27 mA / W and its detectivity is only 9.8×10 7 Jones, performance is limited (see reference [2]). Third, the spectral response range of single or double-layer heterojunctions is usually narrow, making it difficult to cover both visible and near-infrared bands at the same time, which limits the broadband detection capability of the device. For example, ReSe2 / MoS2 heterojunctions perform well at 638 nm visible light, but have a weak response in the near-infrared region (see comparative reference [3]).

[0004] In summary, existing bilayer van der Waals heterojunction photodetectors suffer from fundamental contradictions in terms of interface quality, carrier transport efficiency, and spectral response range, making synergistic optimization difficult. Therefore, a novel heterojunction structure design and fabrication method is urgently needed to synergistically achieve defect passivation, carrier transport modulation, and bandgap engineering at the atomic scale, thereby simultaneously overcoming the integrated challenges of high responsivity, high detectivity, fast response, and broad spectral coverage.

[0005] [1] B. Yan, B. Ning, GX Zhang, DH Zhou, X. Shi, CX Wang, HQ Zhao, Ultra-Thin GeSe / WS2 Vertical Heterojunction with ExcellentOptoelectronic Performances, Advanced Optical Materials 10(6) (2022);

[0006] [2] C. Su, MY Li, H. Yan, Y. Zhang, H. Li, WH Fan, WJ Bai,XJ Liu, QG Wang, SG Yin, PdSe / NbSe Heterojunction Photodetector withBroadband Detection and Polarization Sensitivity, Acs Appl Mater Inter 17(3)(2025) 5213-5222;

[0007] [3] KL Li, CH Du, HL Gao, TH Yin, YK Yu, WJ Wang, Ultra-fast and linear polarization-sensitive photodetectors based on ReSe2 / MoS2 van der Waals heterostructures, J Materiomics 8(6) (2022) 1158-1164. Summary of the Invention

[0008] This invention aims to overcome the shortcomings of existing technologies and provide a sandwich-type van der Waals heterojunction photodetector and its fabrication method. This detector intends to address the three core problems of interfacial recombination, low carrier mobility, and narrow spectral range by ingeniously designing a sandwich structure (pgp) of "p-type rare-earth co-doped transition metal dichalcogenides - g-type graphene - p-type narrow-bandgap transition metal dichalcogenides".

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] In a first aspect, the present invention provides "a sandwich-type van der Waals heterojunction photodetector", comprising a substrate and a first electrode, a photosensitive heterojunction layer and a second electrode sequentially stacked on the substrate;

[0011] The photosensitive heterojunction layer is a sandwich-type van der Waals heterojunction, comprising, from bottom to top:

[0012] 1. A p-type rare-earth co-doped transition metal dichalcogenide layer, namely an erbium / ytterbium co-doped tungsten disulfide layer: This layer has a monolayer or few-layer structure, and the rare-earth elements co-doped with tungsten disulfide preferably include erbium (Er) and ytterbium (Yb), with a total doping atomic percentage of 8% to 15% for Er and Yb. This layer is used for efficient absorption in the visible light band, and passivates intrinsic defects and introduces impurity energy levels through rare-earth doping to broaden the spectral response.

[0013] 2. Graphene Intermediate Layer: This layer is a monolayer of graphene grown by chemical vapor deposition, disposed on top of the p-type rare-earth co-doped transition metal dichalcogenide layer. Utilizing its ultra-high carrier mobility and atomically flat surface, this layer acts as a highly efficient carrier transport channel and interface passivation layer, suppressing interlayer recombination and carrier scattering while maintaining the band structure of the heterojunction.

[0014] 3. p-type narrow bandgap transition metal dichalcogenide layer: disposed on the graphene interlayer, preferably a 2H phase molybdenum ditelluride (MoTe2) layer with a thickness of 30-50 nm. This layer has a narrow bandgap of about 1.0 eV, which is used to extend the detector's response to the near-infrared band and form a good ohmic contact with the metal electrode, reducing dark current.

[0015] Furthermore, in the p-type rare-earth co-doped transition metal dichalcogenide layer, the doping concentration ratio of Er to Yb is 1:1 to 1:2. The substrate is a silicon substrate (SiO2 / Si) with a silicon dioxide layer on its surface.

[0016] The first electrode and the second electrode are chromium (Cr) / gold (Au) composite electrodes, wherein the Cr layer has a thickness of 5-15 nm and the Au layer has a thickness of 40-60 nm, and they form ohmic contacts with the p-type narrow bandgap transition metal dichalcogenide layer and the heavily doped silicon on the substrate, respectively.

[0017] Where / indicates that the molecule is the surface and the denominator is the substrate.

[0018] Secondly, the present invention provides "a method for fabricating a sandwich-type van der Waals heterojunction photodetector", comprising the following steps:

[0019] S1: Prepare a p-type rare-earth co-doped transition metal dichalcogenide layer on a substrate; specifically,

[0020] A dual-temperature zone chemical vapor deposition (CVD) system was used. The sulfur source was placed in the upstream temperature zone, and a precursor mixture containing tungsten trioxide (WO3), sodium chloride (NaCl), erbium trichloride (ErCl3), and ytterbium trichloride (YbCl3) was placed in the downstream temperature zone. A SiO2 / Si substrate was placed upside down on top of the precursor. After evacuating the system, an inert gas was introduced. First, the upstream sulfur zone was heated to 180-200°C to volatilize the sulfur. Then, the downstream precursor zone was heated to 900-1000°C at a rate of 15-25°C / min and maintained in an Ar / H2 mixed atmosphere for 5-15 minutes for reaction growth. After cooling, a monolayer of triangular erbium / ytterbium co-doped tungsten disulfide (WS2:Er / Yb) was obtained on the substrate, which is a p-type rare earth co-doped transition metal dichalcogenide layer.

[0021] S2: Transfer and fix the graphene interlayer on the p-type rare earth co-doped transition metal dichalcogenide layer; specifically,

[0022] S201: A polymethyl methacrylate (PMMA) support layer is spin-coated onto the surface of a monolayer graphene / copper foil grown by chemical vapor deposition. After curing, the copper foil is dissolved using an etching solution to obtain a polymethyl methacrylate-supported graphene film, which is then cleaned with deionized water.

[0023] S202: Using polydimethylsiloxane (PDMS) elastomer as a transfer stamp, the graphene film supported by polymethyl methacrylate is retrieved;

[0024] S203: Under an optical microscope, the graphene on the polydimethylsiloxane stamp is precisely aligned and attached to the erbium / ytterbium co-doped tungsten disulfide surface grown in step S1.

[0025] S204: Gently heat to 70-90°C and hold for 3-8 minutes to enhance interlayer van der Waals forces, then slowly peel off the PDMS stamp;

[0026] S205: The sample was immersed in acetone to dissolve and remove the polymethyl methacrylate support layer. After cleaning and drying, an erbium / ytterbium co-doped tungsten disulfide / graphene (WS2:Er / Yb / Graphene) heterostructure was obtained.

[0027] S3: Transfer and stack p-type narrow bandgap transition metal dichalcogenide layers on the graphene intermediate layer to form an erbium / ytterbium co-doped tungsten disulfide / graphene / molybdenum ditelluride (WS2:Er / Yb / Graphene / MoTe2) sandwich-type heterojunction; specifically,

[0028] S301: Obtain molybdenum ditelluride flakes of the 2H phase by mechanical peeling and attach them to a polydimethylsiloxane stamp;

[0029] S302: Under an optical microscope, precisely align and stack the 2H phase molybdenum ditelluride flakes on the polydimethylsiloxane stamp onto the target area of ​​the graphene surface obtained in step S2.

[0030] S303 undergoes hot pressing treatment under the following conditions: temperature 80-100°C, time 5-15 minutes, to enhance interlayer adhesion and eliminate interface residues.

[0031] S4: Fabricate a first electrode and a second electrode on the sandwich-type heterojunction to realize the fabrication of a photodetector; specifically,

[0032] S401: Electrode patterns are defined on the stacked heterojunction structure using laser direct-write lithography technology;

[0033] S402: Physical vapor deposition method for sequential deposition of metallic chromium and metallic gold layers;

[0034] S403: Excess metal is removed using a stripping process to form the final electrode structure, thus obtaining the sandwich-type van der Waals heterojunction photodetector.

[0035] Furthermore, the etching solution in step S201 is a ferric chloride (FeCl3) solution or a mixed solution of hydrochloric acid (HCl) and copper sulfate (CuSO4).

[0036] Furthermore, in steps S203 and S302, a precision transfer platform with three-dimensional fine-tuning function is used for interlayer alignment.

[0037] Furthermore, after step S303, a rapid thermal annealing step is performed at 150-250°C for 2-10 minutes under an inert atmosphere to further optimize the interface contact.

[0038] The beneficial effects of this invention are as follows: This invention provides a sandwich-type van der Waals heterojunction photodetector and its fabrication method. By constructing a sandwich-type van der Waals heterojunction consisting of "p-type rare-earth co-doped transition metal dichalcogenide - g-type graphene - p-type narrow-bandgap transition metal dichalcogenide", atomic-level integration of defect engineering, carrier transport regulation, and bandgap engineering is synergistically achieved. Specifically, rare-earth co-doping significantly passivates the intrinsic vacancy defects of the transition metal dichalcogenide and broadens its spectral response; graphene is introduced as an ultra-high mobility intermediate layer to effectively suppress interfacial recombination and accelerate carrier extraction; and narrow-bandgap molybdenum distelluride is used to extend the near-infrared response and form a good ohmic contact. This structure enables the device to simultaneously possess ultra-high responsivity (over 200 A / W), high detectivity (over 2.7 × 10¹² Jones), and excellent external quantum efficiency (over 39,000%) in the visible light (635 nm) and near-infrared (980 nm) bands. Moreover, the performance improvement remains stable under different bias voltages. It successfully solves the synergistic optimization problem of traditional two-dimensional heterojunction photodetectors, which have many interface defects, low carrier mobility, and narrow spectral range. It provides a general and feasible technical solution for the design and fabrication of next-generation high-performance broadband optoelectronic devices. Attached Figure Description

[0039] To illustrate the objectives and technical solutions of this invention, the following figures are provided:

[0040] Figure 1 This is a flowchart illustrating the fabrication process of a sandwich-type van der Waals heterojunction photodetector according to Embodiment 1 of the present invention; wherein, Ⅰ is a graphene film pre-treated with etching solution, Ⅱ is PDMS bonded to the graphene film, Ⅲ is the transfer of the graphene film, Ⅳ is the transfer of PDMS with graphene film onto erbium-ytterbium co-doped tungsten disulfide, and Ⅴ is the peeling off of PDMS to obtain an erbium-ytterbium co-doped tungsten disulfide / graphene van der Waals heterojunction. i) Mechanically exfoliating to obtain molybdenum ditelluride (MoD) sheets; ii) PDMS bonding of MoD sheets; iii) Transferring MoD sheets; VI) Transferring MoD sheets onto erbium-ytterbium co-doped tungsten disulfide / graphene; VII) Laser direct writing of the erbium-ytterbium co-doped tungsten disulfide / graphene / MoD van der Waals heterojunction; VIII) Sputtering coating of the erbium-ytterbium co-doped tungsten disulfide / graphene / MoD van der Waals heterojunction.

[0041] Figure 2Figures 1 and 2 show the characterization of the material prepared in Example 1 of this invention. Figures (a) and (b) are comparisons of the photoluminescence and Raman spectra of WS2:Er / Yb and pure WS2, respectively. Figure (c) is the Raman spectrum of the heterojunction. Figures (d) and (e) are the high-resolution transmission electron microscopy (TEM) image and selected area electron diffraction (SED) pattern of WS2:Er / Yb, respectively. Figure (f) is the atomic force microscopy morphology of each component of the sandwich-type heterojunction. Figures (g)-(i) are the thickness diagrams of each component of the sandwich-type heterojunction, respectively.

[0042] Figure 3 Figure 1 shows the structural characteristics of the WS2:Er / Yb / MoTe2 bilayer heterojunction device used for comparative experiments in Example 2 of this invention; wherein, Figure (a) is a flowchart of the fabrication process of the bilayer heterojunction device, Figure (b) is a schematic diagram of its structure, Figure (c) is an optical microscope image of it, and Figure (d) is its current-voltage characteristic curve.

[0043] Figure 4 The figures show the performance of the WS2:Er / Yb / MoTe2 bilayer heterojunction device used in the comparative experiment in Example 2 of the present invention; wherein, Figure (a) is the photocurrent performance figure, Figure (b) is the responsivity performance figure, Figure (c) is the detectivity performance figure, and Figure (d) is the external quantum efficiency performance figure.

[0044] Figure 5 Figure 1 shows the structure and performance of a sandwich-type van der Waals heterojunction photodetector according to Embodiment 2 of the present invention. Figure 2 shows the structure and performance of the detector. Figure 3 shows the structure, Figure 4 shows the optical microscope image, Figure 5 shows the current-voltage characteristic curve, Figures 6-7 show the performance of photocurrent, responsivity and detectivity, respectively, Figure 8 shows the performance comparison with the WS2:Er / Yb / MoTe2 double-layer heterojunction device, and Figure 9 shows the comparison of the optical switching characteristic curves of a sandwich-type van der Waals heterojunction photodetector (pgp) and the WS2:Er / Yb / MoTe2 double-layer heterojunction device (pp) under 635 nm and 980 nm illumination. Detailed Implementation

[0045] Example 1: In biomedical imaging, near-infrared response capability needs to be considered to achieve deep tissue detection; in optical communication, high response speed and wide band compatibility need to be considered to improve data transmission bandwidth and sensitivity. Therefore, addressing the shortcomings of existing technologies, this invention provides "a sandwich-type van der Waals heterojunction photodetector and its fabrication method".

[0046] Combination Figure 1 A method for fabricating a sandwich-type van der Waals heterojunction photodetector includes the following steps:

[0047] S1: Prepare a p-type rare earth co-doped transition metal dichalcogenide layer on a substrate.

[0048] SiO2 / Si wafers (oxide layer thickness 300 nm) grown by thermal oxidation were used as device substrates, and were ultrasonically cleaned with acetone, isopropanol and deionized water in sequence and then dried with nitrogen.

[0049] A dual-temperature zone chemical vapor deposition (CVD) system was used. 120 mg of sulfur powder was placed in the upstream zone, and a uniformly mixed precursor of 60 mg WO3, 5 mg NaCl, 10 mg ErCl3, and 10 mg YbCl3 was placed in the downstream zone. A surface-cleaned SiO2 / Si substrate (300 nm oxide layer thickness) was placed upside down on top of the downstream precursor boat. The system was evacuated to below 5 Pa and then filled with high-purity argon gas to atmospheric pressure. First, the upstream sulfur region was heated to 180°C and held for 5 min to allow the sulfur to fully volatilize. Then, the downstream temperature region was heated to 950°C at a rate of 20°C / min, and an Ar / H2 mixed gas (volume ratio 9:1) with a flow rate of 66 sccm was introduced as both carrier gas and reducing gas. After growing for 10 min, the temperature was rapidly reduced to obtain a monolayer triangular WS2:Er / Yb with a size of approximately 20-100 μm. XPS and EDS confirmed that the total Er / Yb doping concentration was 11.56 at.

[0050] S2: Transfer and fix the graphene interlayer on the p-type rare-earth co-doped transition metal dichalcogenide layer. Specifically,

[0051] S201: PMMA-assisted exfoliation: Spin-coat PMMA (4% in anisole, 500 rpm / 5 s, 3500 rpm / 60 s) onto CVD-grown monolayer graphene / copper foil, and cure by baking at 105°C for 2 minutes. Float the sample on a 1 M FeCl3 solution surface and etch for 1.5 hours to completely remove the copper foil. Rinse three times with deionized water and transfer to a clean water tank for later use.

[0052] S202: PDMS-assisted targeted transfer: The PMMA / graphene film was retrieved using a pre-cured PDMS stamp (SYLGARD 184, 5:1 mixture, cured at 80°C for 1 hour). Under an optical microscope equipped with a CCD camera and a 3D precision micromanipulation platform, the graphene was precisely aligned and adhered to the target WS2:Er / Yb domains.

[0053] S203: Interface Optimization and Support Layer Removal: The bonded sample was placed on an 80°C hot stage for 5 minutes to enhance van der Waals adhesion, followed by slow (approximately 1 mm / s) vertical peeling of the PDMS stamp. The sample was then immersed in acetone for 1 hour to completely dissolve the PMMA, rinsed again with deionized water, and dried with nitrogen to obtain a clean WS2:Er / Yb / Graphene heterostructure.

[0054] S3: A p-type narrow bandgap transition metal dichalcogenide layer is transferred and stacked on the graphene intermediate layer to form a WS2:Er / Yb / Graphene / MoTe2 sandwich-type heterojunction. Specifically,

[0055] S301: A thin film with a thickness of about 40 nm (about 57 layers) was obtained from the 2H-MoTe2 bulk crystal by repeatedly peeling and tearing the “Scotch” tape and then attached to a clean PDMS stamp.

[0056] S302: Under an optical microscope, MoTe2 sheets are precisely stacked onto a designated area on the graphene surface using a micromanipulation platform to ensure complete coverage of the heterojunction active region.

[0057] S303: Hot pressing treatment: Place the sample on a 90°C hot stage for 10 minutes, then slowly cool to room temperature. This process effectively eliminates interlayer gaps and water molecules, enhancing the quality of interfacial bonding.

[0058] S4: Fabricate a first electrode and a second electrode on the sandwich-type heterojunction to realize the fabrication of a photodetector. Specifically,

[0059] S401: Photolithography to define electrodes: Positive photoresist (AZ5214, 4000 rpm / 30 s) is spin-coated onto the stacked sandwich heterojunction. Source and drain electrode patterns are defined using a laser direct-write lithography system (Heidelberg DWL 66+), with a channel length of 10 μm and a width of 5 μm. Clear electrode windows are obtained after development (AZ400K, 30 s).

[0060] S402: Metal Deposition: The sample is fed into the chamber of a magnetron sputtering coating machine (Kurt J. Lesker PVD 75). The background vacuum is better than 5 × 10⁻⁻⁻⁴. 5 Under the condition of Pa, a 10 nm thick Cr layer (adhesion layer) and a 50 nm thick Au layer (conductive layer) were sequentially sputtered and deposited, with a deposition power of 100 W for both layers and an Ar gas working pressure of 0.5 Pa.

[0061] S403: Lifting and Shaping: The sample is immersed in acetone for ultrasonic-assisted lift-off (100 W, 10 minutes) to remove the photoresist and excess metal on top of it, forming the final Cr / Au electrode structure.

[0062] S404: Post-processing: To optimize contact performance, the device is subjected to rapid thermal annealing (200°C, 5 minutes) under argon protection.

[0063] This embodiment presents a sandwich-type van der Waals heterojunction photodetector structure as follows: Figure 5As shown in (a), it includes a SiO2 / Si substrate, a Cr / Au electrode, and a three-layer stacked photosensitive heterojunction layer.

[0064] Its optical microscope images are as follows Figure 5 As shown in (b), a clear layered stacking is visible. The heterojunction, from bottom to top, consists of:

[0065] p-type erbium / ytterbium co-doped tungsten disulfide layer: grown by chemical vapor deposition, with a doping concentration of approximately 11.56 at% (Er:Yb ≈ 1:1.5) and a thickness of approximately 1 nm (monolayer).

[0066] g-type graphene intermediate layer: a monolayer of graphene grown by CVD method, with a thickness of approximately 0.7 nm;

[0067] p-type 2H phase molybdenum distellide layer: obtained by mechanical exfoliation, with a thickness of approximately 40 nm (approximately 57 layers).

[0068] Specific material characterization diagrams, such as Figure 2 As shown. Figure 2 (a) Photoluminescence (PL) spectra show that, compared with pure WS2, the emission peak of WS2:Er / Yb is redshifted by about 6.5 nm and the intensity is about twice as strong, confirming that rare earth doping introduces impurity energy levels and passivates defects; Figure 2 In the Raman spectrum of (b), the A1g peak of WS2:Er / Yb shifted from 416.3 cm⁻¹ in pure WS2 to 418.6 cm⁻¹, indicating lattice strain and enhanced peak intensity, suggesting improved structural order. Figure 2 High-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) patterns confirmed that the WS2:Er / Yb single crystals were of good quality and exhibited local lattice distortion (<2% strain). Figure 2 (c) shows the complete WS2:Er / Yb, graphene (G peak and 2D peak) and MoTe2 characteristic peaks without significant shift, proving that a high-quality van der Waals interface was formed. Figure 2 (f)- Figure 2 (i) The atomic force microscopy image clearly shows the step-like morphology of the heterostructure and the thickness of each layer was quantitatively measured: WS2:Er / Yb is about 1 nm (monolayer), graphene is about 0.7 nm (monolayer), and MoTe2 is about 40 nm.

[0069] After preparation, the sandwich-type van der Waals heterojunction photodetector prepared in this embodiment was tested using a Keysight B1500A semiconductor parameter analyzer and a 635 nm and 980 nm adjustable power laser source.

[0070] Combination Figure 5As can be seen, the photodetector prepared by the method of this invention has a responsivity of up to 201.33 A / W in the 635 nm band and a bias voltage of -5 V, an external quantum efficiency (EQE) exceeding 39000%, and a response time on the order of microseconds. This ultra-high responsivity and high gain characteristic means that when receiving weak light signals, the gain requirements of subsequent amplifiers can be significantly reduced, simplifying receiver design and improving the system signal-to-noise ratio, making it particularly suitable for high-speed visible light communication (VLC) systems.

[0071] The photodetector prepared by the method of this invention still achieves a responsivity of 3.55 A / W and a detectivity (D*) of 5.77 × 10¹ at the 980 nm near-infrared bio-optical window. 0 Jones. This performance demonstrates that the device can efficiently detect weak fluorescence or scattering signals generated by biological tissues in this wavelength range. At the same time, its excellent visible light response is also compatible with common fluorescent dye labels (such as FITC and Rhodamine), providing core device support for the development of broadband, highly sensitive portable biosensing and imaging devices.

[0072] Example 2: To better demonstrate the beneficial effects of the present invention, a comparative experiment was designed in this example. The method of the present invention was compared with a WS2:Er / Yb / MoTe2 bilayer heterojunction device without a graphene interlayer to quantitatively reveal the key role of graphene.

[0073] The fabrication process of the WS2:Er / Yb / MoTe2 bilayer heterojunction device is as follows: Figure 4 As shown in (a), its structural schematic diagram and optical microscope image are respectively as follows: Figure 4 (b) and Figure 4 (c).

[0074] The bilayer heterojunction device used for the comparative experiment was prepared in almost the same way as the sandwich-type heterojunction device of the present invention: WS2:Er / Yb grown by CVD in the same batch as in Example 1 and mechanically exfoliated MoTe2 (~40 nm); except that the graphene transfer step was omitted. Similarly, the same PDMS-assisted dry transfer technique as in Example 1 was used to directly stack the MoTe2 sheets onto the WS2:Er / Yb surface and hot-press them at 90°C for 10 minutes; and the electrodes were prepared using the same laser direct-write lithography, magnetron sputtering (10 nm Cr / 50 nm Au) and exfoliation process as in Example 1, with the channel size remaining consistent (10 μm × 5 μm). The post-processing was also performed using the same rapid thermal annealing (200°C, 5 minutes, Ar atmosphere).

[0075] Figure 4(d) shows the I_DS-V_DS curves of this double-layer heterojunction device, whose symmetry reflects the characteristics of the pp junction. Under 635 nm illumination and a -5 V bias, the device's performance is as follows: Figure 5 (a)- Figure 5 As shown in (d), the photocurrent is 195.34 nA, the responsivity is 15.4 AW⁻¹, the specific detectivity is 1.52 × 10¹² Jones, and the external quantum efficiency is 3013.81%. Under 980 nm illumination, its responsivity is only 0.47 AW⁻¹.

[0076] Under identical testing conditions (room temperature, atmospheric environment, light source power density 0.6-115.9 mW / cm²), the bilayer (pp) device and the sandwich (pgp) device of Example 1 were tested in parallel. Key performance parameters are compared in Table 1 below:

[0077] Table 1: Performance Comparison of Double-Layer Heterojunction (PP) and Sandwich-Layer (PGP) Heterojunction Photodetectors

[0078]

[0079] Combination Figure 5 As shown in (h), at 635 nm, the introduction of a graphene interlayer increased the device responsivity from 15.4 A / W to 201.33 A / W, an increase of more than an order of magnitude. This directly proves that graphene, as an ultrafast carrier transport channel, effectively solves the problems of low carrier mobility and severe interface recombination in bilayer structures, and is the fundamental reason for the huge improvement in responsivity and EQE.

[0080] In the 980 nm near-infrared band, the responsivity of the PGP device also achieved a significant 7.6-fold improvement. This indicates that the graphene layer not only accelerates carrier extraction, but its excellent light transmittance and interface passivation also ensure that infrared photogenerated carriers contributed by the narrow bandgap absorption of MoTe2 and the WS2:Er / Yb impurity energy levels can be efficiently collected, achieving true visible-near-infrared synergistic enhancement.

[0081] Comparative experimental data clearly demonstrate that the sandwich-type heterojunction structure designed in this invention is not a simple material stacking, but rather a qualitative change. This effect enables the device to achieve ultra-high responsivity while maintaining high detectivity (low noise). This characteristic is crucial for applications requiring both high sensitivity and high signal-to-noise ratio, such as low-light environment monitoring (e.g., nighttime remote sensing) and high dynamic range imaging. In contrast, while bilayer heterojunction devices offer certain performance characteristics, they struggle to meet the demands of these high-end applications in key indicators such as responsivity.

[0082] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A sandwich-type van der Waals heterojunction photodetector, comprising a substrate and a first electrode, a photosensitive heterojunction layer, and a second electrode disposed on the substrate, characterized in that, The photosensitive heterojunction layer is a sandwich-type van der Waals heterojunction, which includes, from bottom to top: p-type rare earth co-doped transition metal dichalcogenide layer; Graphene intermediate layer; p-type narrow bandgap transition metal dichalcogenide layer; Wherein, the p-type rare earth co-doped transition metal dichalcogenide layer is a single layer or a few layers of tungsten disulfide, and the co-doped rare earth elements include erbium and ytterbium, i.e., erbium / ytterbium co-doped tungsten disulfide; / indicates that the molecular material is the surface and the denominator material is the substrate.

2. The sandwich-type van der Waals heterojunction photodetector according to claim 1, characterized in that, The total percentage of doped atoms of the rare earth elements erbium and ytterbium is 8% to 15%, and the doping atom concentration ratio of erbium to ytterbium is 1:1 to 1:

2.

3. A sandwich-type van der Waals heterojunction photodetector according to claim 1 or 2, characterized in that, The p-type narrow bandgap transition metal dichalcogenide layer is molybdenum ditelluride in the 2H phase with a thickness of 30 to 50 nanometers; the graphene interlayer is a single-layer graphene grown by chemical vapor deposition; the substrate is a silicon substrate with an oxide layer on its surface; the first electrode and the second electrode are composite electrodes composed of a chromium layer and a gold layer, wherein the chromium layer has a thickness of 5 to 15 nanometers and the gold layer has a thickness of 40 to 60 nanometers.

4. A method for fabricating a sandwich-type van der Waals heterojunction photodetector, characterized in that, Includes the following steps: S1. Prepare a p-type rare earth co-doped transition metal dichalcogenide layer on the substrate; S2. Transfer and fix the graphene interlayer on the p-type rare earth co-doped transition metal dichalcogenide layer. S3. Transfer and stack p-type narrow bandgap transition metal dichalcogenide layers on the graphene intermediate layer to form a sandwich-type heterojunction; S4. Prepare a first electrode and a second electrode on the sandwich-type heterojunction.

5. The method for fabricating a sandwich-type van der Waals heterojunction photodetector according to claim 4, characterized in that, Step S1 specifically includes: A dual-temperature zone chemical vapor deposition method is used, in which the sulfur source is placed in the upstream temperature zone, the precursor mixture containing tungsten trioxide, sodium chloride, erbium trichloride and ytterbium trichloride is placed in the downstream temperature zone, and the substrate is placed on top of the precursor in the downstream temperature zone; In an inert gas or a mixture of inert gas and hydrogen, the upstream temperature zone is first heated to 180°C to 200°C to volatilize sulfur, and then the downstream temperature zone is heated to 900°C to 1000°C for reaction growth, thereby obtaining a single layer of triangular erbium / ytterbium co-doped tungsten disulfide on the substrate, which is a p-type rare earth co-doped transition metal dichalcogenide layer.

6. The method for fabricating a sandwich-type van der Waals heterojunction photodetector according to claim 4, characterized in that, Step S2 specifically includes: S201. A polymer support layer is spin-coated onto the surface of a single-layer graphene grown on a copper foil. After curing, the copper foil is dissolved and removed to obtain a polymer-supported graphene film, which is then cleaned. S202, Use an elastomer transfer stamp to retrieve the graphene film; S203. Under microscopic observation, the graphene film is aligned and attached to the surface of the p-type rare earth co-doped transition metal dichalcogenide layer. S204. Perform heat treatment to enhance interlayer bonding, and then remove the elastomer transfer stamp; S205. Dissolve and remove the polymer support layer to obtain a heterostructure of erbium / ytterbium co-doped tungsten disulfide / graphene.

7. The method for fabricating a sandwich-type van der Waals heterojunction photodetector according to claim 6, characterized in that, The elastomeric transfer stamp is a polydimethylsiloxane stamp; the heat treatment temperature is 70°C to 90°C, and the time is 3 to 8 minutes.

8. The method for fabricating a sandwich-type van der Waals heterojunction photodetector according to claim 4, characterized in that, Step S3 specifically includes: p-type narrow bandgap transition metal dichalcogenide thin films were obtained by mechanical exfoliation. The sheet was picked up using an elastomer transfer stamp; Under microscopic observation, the thin film is precisely aligned and stacked onto the target area on the surface of the graphene interlayer; The process involves hot pressing at a temperature of 80°C to 100°C for 5 to 15 minutes.

9. The method for fabricating a sandwich-type van der Waals heterojunction photodetector according to claim 4, characterized in that, Following step S3, the process further includes annealing the sandwich-type heterojunction in an inert atmosphere at a temperature of 150°C to 250°C for 2 to 10 minutes.

10. The method for fabricating a sandwich-type van der Waals heterojunction photodetector according to claim 4, characterized in that, Step S4 specifically includes: Electrode patterns were defined on the sandwich-type heterojunction using laser direct-write lithography. A chromium layer and a gold layer were deposited sequentially using physical vapor deposition. The first and second electrodes are formed by a stripping process.

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