High-responsivity broadband Van der Waals heterojunction photoelectric detector and preparation method thereof

Abstract

The invention discloses a high-responsivity broadband Van der Waals heterojunction photoelectric detector and a preparation method thereof, and belongs to the technical field of semiconductor photoelectric devices. The detector comprises a bearing substrate, an erbium-doped tungsten disulfide single-layer film, a molybdenum ditelluride nanosheet and a metal electrode from bottom to top. The preparation method comprises the following steps: growing an erbium-doped tungsten disulfide film by adopting a chemical vapor deposition method; mechanically stripping to obtain a molybdenum ditelluride nanosheet; an erbium-doped tungsten disulfide / molybdenum ditelluride vertical heterojunction is constructed through a micro-area fixed-point dry transfer technology; and finally, manufacturing the electrode by adopting a micro-nano machining process. The intrinsic defect of tungsten disulfide is effectively passivated through erbium doping, efficient separation and transportation of photon-generated carriers are synergistically realized by combining with a Type-II energy band alignment heterojunction formed by molybdenum ditelluride, dark current is greatly inhibited, the detector has broadband from visible light to near-infrared light and high-sensitivity detection capability, and the detector can be applied to the field of visible light detection and near-infrared light detection. The method has important application value in the fields of integrated optoelectronic chips, multispectral sensing and the like.

Description

Technical Field

[0001] This invention relates to a high-response-rate broadband van der Waals heterojunction photodetector and its fabrication method, belonging to the field of semiconductor optoelectronic device technology, and is particularly applicable to high-response-rate broadband van der Waals heterojunction photodetectors and their fabrication. Background Technology

[0002] Broadband photodetectors, as core components of modern optoelectronic systems, convert light signals of different wavelengths into electrical signals, making them crucial for multispectral sensing, information processing, and communication. With the rapid development of fields such as biomedical imaging, autonomous driving lidar, high-speed optical communication, and flexible wearable electronics, there is an urgent need for miniaturized, integrated, high-performance, and wide-spectral-response photodetectors. Achieving broadband, high-sensitivity detection from visible light to near-infrared promises the integration of multiple functions on a single chip, overcoming the bottlenecks of large size, high power consumption, and integration difficulties in traditional multi-device systems. This has significant strategic importance and application value.

[0003] Two-dimensional materials, represented by transition metal chalcogenides, offer an ideal material platform for constructing next-generation high-performance photodetectors due to their atomic-level thickness, absence of dangling bonds, tunable band gaps, and excellent photoelectric properties. Chemical vapor deposition (CVD) technology can mass-produce large-area, high-quality single crystals of two-dimensional materials. To extend the detection range to the near-infrared band, two-dimensional materials with narrow band gaps (such as molybdenum ditelluride, with a band gap of approximately 1.05 eV) have attracted widespread attention. However, existing technologies face multiple challenges: First, during material growth (especially in CVD), intrinsic structural defects such as vacancies are inevitably introduced. These defects act as non-radiative recombination centers, severely reducing carrier lifetime, mobility, and the separation and collection efficiency of photogenerated carriers, ultimately limiting device responsivity and detection sensitivity. Second, while heterojunction detectors based on narrow band gap materials offer a wide spectral range, they often suffer from problems such as excessively high dark current, inhomogeneous crystal quality, or low carrier separation efficiency at the heterojunction interface, hindering further improvements in their overall performance (especially specific detectivity). Furthermore, while chemical doping can adjust material properties, systematic research on deeply integrating rare earth ion doping with van der Waals heterojunction bandgap engineering to optimize broadband photoelectric detection performance through synergistic effects is still insufficient. In particular, there is a lack of effective technical solutions and clear preparation paths for how to simultaneously improve intrinsic material defects and heterojunction interface carrier transport through doping.

[0004] Therefore, existing broadband photodetectors based on two-dimensional materials have shortcomings in key areas such as defect suppression, interface quality control, and efficient photoelectric conversion within a wide spectral band. There is an urgent need to develop innovative material modification methods and device structure designs to achieve novel photodetectors that combine excellent performance characteristics such as wide spectral response, ultra-high responsivity, high specific detectivity, and low dark current. Summary of the Invention

[0005] To address the problems of low responsivity, high dark current in narrow bandgap material heterojunctions, and uneven photoelectric conversion efficiency in existing two-dimensional material photodetectors due to intrinsic defects, this invention provides a high-responsivity broadband van der Waals heterojunction photodetector and its fabrication method. The aim is to effectively passivate material defects through in-situ erbium doping and combine it with a Type-II band-aligned pp heterojunction design to achieve high-performance and stable photoelectric detection from the visible to near-infrared bands.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides "a high-response-rate broadband van der Waals heterojunction photodetector", characterized in that the detector comprises, from bottom to top:

[0008] Supporting substrate;

[0009] Erbium-doped tungsten disulfide monolayer film located on the substrate surface;

[0010] Molybdenum ditelluride nanosheets are transferred and stacked on the erbium-doped tungsten disulfide monolayer film and form a clean interface with it;

[0011] And metal electrodes that form Schottky contacts with the erbium-doped tungsten disulfide monolayer film and the molybdenum ditelluride nanosheets, respectively;

[0012] The erbium-doped tungsten disulfide monolayer film is a p-type semiconductor material synthesized by in-situ chemical vapor deposition. Erbium ions are incorporated into the tungsten disulfide lattice through substitutional doping. The molybdenum ditelluride nanosheets are also p-type semiconductor materials. The erbium-doped tungsten disulfide monolayer film and the molybdenum ditelluride nanosheets are bonded together by van der Waals forces to form a vertical p-type homo-heterojunction with Type-II (interleaved) band alignment. This band structure creates a built-in electric field at the interface that facilitates the separation of photogenerated carriers.

[0013] Preferably, the atomic percentage of the doping concentration of the erbium ions (erbium ions) is between 8% and 12%. This concentration range achieves an optimal balance between effectively compensating for tungsten (W) vacancy defects and avoiding the introduction of excessive lattice distortion.

[0014] Preferably, the metal electrode consists of an adhesion layer and a conductive layer, which are chromium / gold (Cr / Au) stacks, wherein the chromium layer has a thickness of 5-15 nanometers and the gold layer has a thickness of 40-70 nanometers.

[0015] Preferably, the substrate is a silicon (Si) wafer with a silicon dioxide (SiO2) insulating layer thermally grown on its surface, and the thickness of the silicon dioxide layer is 280-320 nanometers.

[0016] Where / indicates that the molecule is the surface and the denominator is the substrate.

[0017] Secondly, the present invention provides "a method for fabricating a high-response-rate broadband van der Waals heterojunction photodetector", comprising the following steps:

[0018] S1: Erbium-doped tungsten disulfide monolayer films were prepared using a dual-temperature zone tubular chemical vapor deposition (CVD) method.

[0019] The specific steps are as follows:

[0020] S101: Place sulfur powder with a purity >99.5% in a ceramic boat in the upstream low-temperature zone (first temperature zone);

[0021] S102: Tungsten trioxide powder (WO3) with a purity >99.95%, sodium chloride powder (sodium chloride) with a purity >99.99%, and erbium trichloride powder (ErCl3) are accurately weighed and thoroughly ground and mixed in a mass ratio of 30:2:5 to obtain a mixed precursor, which is placed in the center of a ceramic boat in the downstream high-temperature zone (second temperature zone).

[0022] S103: Evacuate the tubular furnace cavity to below 5 Pascals, then introduce high-purity argon gas to atmospheric pressure, repeating this process several times to remove air.

[0023] S104: An inverted silicon dioxide / silicon substrate with a clean surface is placed over a ceramic boat containing the hybrid precursor and then placed in a tube furnace.

[0024] S105: Under the atmosphere of a continuously purged argon (Ar)-hydrogen (H2) mixed carrier gas, the sulfur region is heated and stabilized at 180-220℃. The mixed precursor region is then heated to a growth temperature of 940-960℃ at a rate of 15-20℃ / min, and held at this temperature for 8-12 minutes for chemical reaction and crystal growth. After the reaction is complete, heating is stopped, and the mixture is allowed to cool naturally to room temperature under the protection of the argon-hydrogen mixed carrier gas, thus obtaining an erbium-doped tungsten disulfide monolayer film with a regular triangular morphology on the substrate. The argon-hydrogen mixed carrier gas contains 90% argon and 10% hydrogen, with a total flow rate of 68 standard cubic centimeters per minute.

[0025] Step 2: Prepare molybdenum ditelluride nanosheets using a mechanical exfoliation method.

[0026] The specific steps are as follows:

[0027] S201: Adhere the molybdenum distellide bulk material to the surface of the blue film;

[0028] S202: By repeatedly folding, pasting, and peeling the blue film, the number of layers of molybdenum distellide bulk material is gradually reduced, thus achieving "thinning".

[0029] S203: Using polydimethylsiloxane gel blocks as a pickup medium, a 5-50 nm thick, clean molybdenum ditelluride thin layer is selectively picked up from the blue film to obtain the desired molybdenum ditelluride nanosheets.

[0030] Preferably, the blue film is a polyacrylate tape.

[0031] Step 3: Construct van der Waals heterojunctions using micro-area fixed-point dry transfer technology.

[0032] The specific steps are as follows:

[0033] S301: On a micromanipulation platform equipped with a high-precision three-dimensional micro-motion stage and heating module, a substrate with an erbium-doped tungsten disulfide monolayer film grown on it is fixed.

[0034] S302: The polydimethylsiloxane gel with molybdenum ditelluride nanosheets attached is mounted on a micro-movement stage and precisely aligned with the target erbium-doped tungsten disulfide monolayer film under an optical microscope.

[0035] S303: Slowly reduce the polydimethylsiloxane gel to allow the molybdenum ditelluride nanosheets to come into gentle contact with the surface of the erbium-doped tungsten disulfide monolayer film;

[0036] S304: Heat the sample stage to 115-125℃ and maintain it for 10-15 minutes to enhance interfacial adhesion with heat assistance, ensuring that the heterojunction interface is tight and clean.

[0037] S305: The polydimethylsiloxane gel is slowly lifted, and the molybdenum ditelluride nanosheets remain on the substrate due to the stronger van der Waals forces with the erbium-doped tungsten disulfide monolayer film, thus forming a vertically stacked van der Waals heterojunction.

[0038] Step 4: Fabricate metal electrodes using micro-nano fabrication techniques.

[0039] The specific steps are as follows:

[0040] S401: Spin-coat photoresist onto the van der Waals heterojunction sample constructed in step S3, use laser direct writing lithography or electron beam lithography, and use tetramethylammonium hydroxide for development to define electrode patterns in specific regions of the van der Waals heterojunction.

[0041] S402: A layer of chromium as an adhesion layer and a layer of gold as a conductive layer are deposited sequentially using electron beam evaporation or magnetron sputtering equipment.

[0042] S403: Use organic solvents such as acetone to strip away the metal in areas not protected by photoresist, leaving the designed metal electrode pattern, and complete the fabrication of the device.

[0043] The beneficial effects of this invention are as follows: This invention provides a high-response-rate broadband van der Waals heterojunction photodetector and its fabrication method. By effectively passivating the intrinsic defects of tungsten disulfide through in-situ doping with rare-earth erbium ions, its crystal quality and photoelectric activity are significantly improved. Simultaneously, by precisely stacking it with narrow-bandgap molybdenum telluride, a pp-type van der Waals heterojunction with Type-II band alignment is constructed. This structure forms a strong built-in electric field at the interface, achieving efficient separation and transport of photogenerated carriers and greatly suppressing dark current. Ultimately, the fabricated device exhibits excellent comprehensive performance in both the visible and near-infrared bands, characterized by ultra-high responsivity, high specific detectivity, and low dark current, achieving broadband, high-sensitivity detection from the visible to near-infrared range. This provides an innovative device solution for next-generation high-performance integrated optoelectronic systems. Attached Figure Description

[0044] To illustrate the objectives and technical solutions of this invention, the following figures are provided:

[0045] Figure 1 This is a flowchart of a method for fabricating a high-response-rate broadband van der Waals heterojunction photodetector according to Embodiment 1 of the present invention;

[0046] Figure 2 The diagram shows the structure and optical diagram of a high-response-rate broadband van der Waals heterojunction photodetector according to Embodiment 1 of the present invention; wherein, (a) is a schematic diagram of the structure of a high-response-rate broadband van der Waals heterojunction photodetector; and (b) is an optical diagram of an erbium-doped tungsten disulfide / molybdenum ditelluride heterojunction.

[0047] Figure 3 The image shows the characterization of the erbium-doped tungsten disulfide material in Example 1 of the present invention; wherein, (a) is the photoluminescence pattern of erbium-doped tungsten disulfide and intrinsic tungsten disulfide; (b) is the projection electron microscope image of erbium-doped tungsten disulfide; and (c) is the X-ray diffraction pattern of erbium-doped tungsten disulfide and intrinsic tungsten disulfide.

[0048] Figure 4 The diagram shows the structural characterization of the erbium-doped tungsten disulfide / molybdenum ditelluride van der Waals heterojunction in Example 1 of the present invention; wherein, (a) is the Raman spectrum of the erbium-doped tungsten disulfide / molybdenum ditelluride heterojunction photodetector; and (b) is the atomic force microscopy probe image of the erbium-doped tungsten disulfide / molybdenum ditelluride heterojunction photodetector.

[0049] Figure 5The following are the photoelectric performance test curves of the erbium-doped tungsten disulfide / molybdenum ditelluride van der Waals heterojunction in Example 2 of the present invention; wherein, (a) is the transfer characteristic curve of the erbium-doped tungsten disulfide / molybdenum ditelluride heterojunction photodetector; (b) is the optical switching characteristic of the erbium-doped tungsten disulfide / molybdenum ditelluride heterojunction photodetector under 980nm illumination; (c) is the responsivity as a function of optical power density; and (d) is the specific detectivity as a function of optical power density.

[0050] Figure 6 The images show the optical diagram and photoelectric performance test curves of the intrinsic tungsten disulfide / molybdenum ditelluride heterojunction photodetector in Embodiment 3 of the present invention; wherein, (a) is the optical diagram of the intrinsic tungsten disulfide / molybdenum ditelluride heterojunction photodetector; (b) is the transfer characteristic curve of the intrinsic tungsten disulfide / molybdenum ditelluride heterojunction photodetector; (c) is the graph showing the change in responsivity with optical power density; and (d) is the graph showing the change in specific detectivity with optical power density.

[0051] Figure 7 This is a schematic diagram of the band structure and carrier transport mechanism of the erbium-doped tungsten disulfide / molybdenum ditelluride heterojunction under different bias and illumination conditions in Embodiment 3 of the present invention; wherein, (a) corresponds to the calculated band alignment of the erbium-doped tungsten disulfide / molybdenum ditelluride heterojunction; (b) corresponds to the erbium-doped tungsten disulfide / molybdenum ditelluride heterojunction under zero bias and darkness; (c) corresponds to the forward bias and darkness; (d) corresponds to the reverse bias and darkness; (e) corresponds to the forward bias and laser illumination; and (f) is the band structure under reverse bias and laser illumination. Detailed Implementation

[0052] Example 1: In next-generation optical communication receivers and on-chip spectrometers, there is an urgent need for photodetector units capable of simultaneously processing visible and near-infrared signals on a small area. Traditional solutions require integrating multiple detectors made of different materials, leading to complex fabrication processes and severe crosstalk. This example aims to provide "a high-response rate broadband van der Waals heterojunction photodetector and its fabrication method," demonstrating how to fabricate a high-performance, broadband photodetector that can serve as a basic "pixel" or "receiving unit" to meet the stringent requirements of high-density integrated optoelectronic chips for the performance and compatibility of core devices.

[0053] Combination Figure 1 A method for fabricating a high-response-rate broadband van der Waals heterojunction photodetector specifically includes the following steps:

[0054] S1: Synthesis of erbium-doped tungsten disulfide (WS2:Er) monolayer film.

[0055] A dual-temperature zone tubular chemical vapor deposition system was employed. Specifically, 60 mg of high-purity sulfur powder was placed in a quartz boat in the upstream temperature zone. In the downstream temperature zone, 30 mg of tungsten trioxide, 2 mg of sodium chloride (as a growth promoter), and 5 mg of erbium trichloride (as a dopant source) were precisely weighed and thoroughly mixed, and placed in the center of another quartz boat. A silicon substrate with 300 nm of silica thermally grown on its surface was inverted and placed above this mixed precursor boat. After evacuation and argon purging, growth was carried out in an argon / hydrogen mixture (90% / 10%, total flow rate 68 standard cubic centimeters per minute): the sulfur zone was heated to 200 °C and held, while the precursor zone was programmed to heat to 950 °C at a rate of 18 °C / min and held at that temperature for 10 minutes. After the reaction, the substrate was allowed to cool naturally, resulting in regular triangular monolayer erbium-doped tungsten disulfide crystals on the substrate. Atomic force microscopy characterized the thickness as approximately 0.9 nm. X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy confirmed that erbium ions were uniformly incorporated into tungsten disulfide lattice vacancies at a concentration of approximately 9.8 at%.

[0056] Specifically, such as Figure 3 (a) Photoluminescence (PL) spectrum shows that the PL peak intensity of WS2:Er is significantly enhanced and redshifted compared to intrinsic tungsten disulfide (WS2), proving that erbium doping effectively improves the light emission efficiency of the material and fine-tunes the band structure. Figure 3 (b) High-resolution transmission electron microscopy (HR-TEM) images show clear lattice fringes of WS2:Er, confirming its high-quality single-crystal properties. Figure 3 The X-ray diffraction (XRD) spectrum comparison in (c) shows that WS2:Er retains the crystal structure of WS2 and shows the characteristic peak of Er2S3, confirming the successful doping of erbium.

[0057] S2: Preparation of molybdenum ditelluride (MoTe2) nanosheets.

[0058] A mechanical peeling method was used. Bulk molybdenum distelluride crystals were adhered to polyacrylate tape (blue film), and the tape was repeatedly folded to reduce the number of layers. Finally, a few-layer molybdenum distelluride sheet with a thickness of approximately 24 nanometers was picked up from the tape using pre-cured polydimethylsiloxane gel.

[0059] S3: Precise construction of erbium-doped tungsten disulfide / molybdenum ditelluride (WS2:Er / MoTe2) vertical heterostructures:

[0060] This step was performed on a micromanipulation platform integrating a high-precision three-dimensional piezoelectric displacement stage and a digitally temperature-controlled hot stage. First, a substrate with erbium-doped tungsten disulfide (TDS) grown on the hot stage was fixed. Then, a polydimethylsiloxane gel with attached molybdenum ditelluride (MoD) nanosheets was manipulated under optical microscopy, aligned with sub-micron precision, and gently placed in the center of the target TDS triangular region. Subsequently, the hot stage was heated to 120°C and held for 10 minutes to enhance interfacial van der Waals interactions and remove interfacial adsorbates. After slowly lifting the gel, MoD was successfully transferred, forming a clean van der Waals heterojunction with an overlap area of ​​approximately 310 square micrometers with the TDS. Raman surface scanning mapping confirmed the simultaneous presence of characteristic peaks of both TDS and MoD at the interface, with no impurity peaks.

[0061] Specifically, Figure 2 (b) The optical microscope (OM) image clearly shows the morphology of the final heterojunction. Figure 4 (a) The Raman spectrum confirms that the heterojunction region contains both characteristic peaks of WS2:Er and MoTe2, and no impurity peaks. Figure 4 (b) Atomic force microscopy (AFM) images accurately measured the thickness of each region of the heterojunction, confirming the stacked structure of monolayer WS2:Er and few-layer MoTe2.

[0062] S4: Electrode fabrication and device completion:

[0063] Standard micro / nano fabrication processes were employed. First, laser direct-write lithography was used, followed by development with 2.38% tetramethylammonium hydroxide for 60 seconds to define the electrode pattern in the heterojunction region (the two electrodes contact the edges of erbium-doped tungsten disulfide and molybdenum ditelluride, respectively). Subsequently, a 10-nanometer chromium layer (adhesion layer) and a 50-nanometer gold layer (conductive layer) were sequentially deposited using electron beam evaporation. Finally, acetone was used for lift-off to form the final metal electrodes, completing the device fabrication.

[0064] This embodiment successfully fabricated a high-response-rate broadband van der Waals heterojunction photodetector, combined with... Figure 2 (a) The detector comprises, from bottom to top:

[0065] Supporting silicon dioxide / silicon substrate;

[0066] Erbium-doped tungsten disulfide monolayer film located on the substrate surface;

[0067] Molybdenum ditelluride nanosheets are transferred and stacked on the erbium-doped tungsten disulfide monolayer film and form a clean interface with it;

[0068] A metal electrode array that forms Schottky contacts with the erbium-doped tungsten disulfide monolayer film and molybdenum ditelluride nanosheets constitutes a two-terminal photodetector.

[0069] The erbium-doped tungsten disulfide monolayer film is a p-type semiconductor material synthesized by in-situ chemical vapor deposition, with the chemical formula erbium-doped tungsten disulfide. Erbium ions are incorporated into the tungsten disulfide lattice through substitutional doping. The molybdenum ditelluride nanosheets are also p-type semiconductor materials. The erbium-doped tungsten disulfide monolayer film and the molybdenum ditelluride nanosheets are bonded together by van der Waals forces to form a vertical p-type homo-heterojunction with Type-II (interleaved) band alignment. This band structure creates a built-in electric field at the interface that facilitates the separation of photogenerated carriers.

[0070] Its core structure lies in the vertical stacking of a p-type erbium-doped tungsten disulfide monolayer and a p-type molybdenum ditelluride few-layer through an atomically clean van der Waals interface, forming an intrinsic Type-II band-aligned heterojunction. This structure eliminates the need for complex doping in traditional semiconductor processes, exhibits good compatibility with silicon-based processes, and achieves highly efficient carrier separation and transport solely through the band differences in the materials themselves and the modulation by erbium ion doping, laying the foundation for the subsequent fabrication of large-scale detector arrays.

[0071] Example 2: In environmental monitoring, smart agriculture, and wearable health devices (such as pulse oximeters), it is often necessary to simultaneously acquire information in the visible light and specific near-infrared bands. Existing devices typically use multiple discrete photodetectors with filters, resulting in large module size, high power consumption, and high cost. This example integrates a high-response-rate broadband van der Waals heterojunction photodetector prepared according to this invention as the core sensing element into a miniaturized multispectral sensing system, verifying its practical application capabilities in real-time, dual-band optical signal differentiation and measurement.

[0072] Step 1: Device Performance Benchmarking and System Adaptation

[0073] Several "high-response-rate broadband van der Waals heterojunction photodetectors" prepared in Example 1 were screened, and one with good performance consistency was selected. This one was placed in a shielded probe station and connected to a semiconductor parameter analyzer (Keithley 2636B) for system-level parameter calibration. The specific calibration parameters are as follows:

[0074] (1) Dark characteristics and noise substrate: Under a bias voltage of ±0.5 V, the dark current is as low as ±33 pA and the equivalent noise power is extremely low, ensuring the high sensitivity of the system.

[0075] (2) Dual-band response calibration: Calibration was performed using 635 nm (representing red light in blood oxygen monitoring) and 980 nm (representing infrared light in blood oxygen monitoring) laser sources. Under optimized bias, the device exhibited high responsivity in both bands (20.7 A·W, respectively). -1 and 0.57 A·W -1It exhibits good linearity and stable, repeatable response, as demonstrated by photoelectric switch testing.

[0076] Step 2: Construct a miniaturized multispectral sensing system, which includes: (1) a photodetector prepared by the method of the present invention as a sensing head; (2) a dual-channel low-noise transimpedance amplifier controlled by a microprocessor, corresponding to the two working bias points of the device (optimizing visible light and near-infrared response); (3) two independently switchable LED light sources (635 nm and 980 nm) as analog signal sources; (4) a microprocessor used to control the switching of light sources, acquire the amplified voltage signal and process it.

[0077] The device performance was tested using a semiconductor parameter analyzer in a shielded probe station. The specific performance results are as follows:

[0078] 1. Dark properties and transfer curves: Figure 5 The transfer characteristic curve (I_ds-V_g) of (a) shows the device’s good gate control characteristics and extremely low off-state current.

[0079] 2. Visible light response (635 nm): at -5 V bias, 0.45 mW·cm⁻¹ -2 At optical power density, the device exhibits excellent photoelectric response. Figure 5 (c) and Figure 5 (d) Shows the trends of responsivity and specific detectivity with optical power density, reaching a peak at low light intensity (20.7 A·W). -1 and 2.72×10 12 Jones).

[0080] 3. Near-infrared response (980 nm): Figure 5 (b) The optical switching characteristic curves demonstrate that the device has a stable and repeatable response under 980 nm illumination, with a responsivity of 0.57 A·W. -1 .

[0081] 4. Band structure mechanism: Figure 7 (a) The calculated band alignment diagram visually demonstrates the Type-II band structure formed between WS2:Er and MoTe2, which is the physical basis for the high performance of the device. Figure 7 (b)- Figure 7 (f) illustrates in detail the energy band diagram of carrier separation and transport mechanisms at the interface under different bias voltages and illumination conditions.

[0082] The multispectral sensing system will then be applied to the following two scenarios to demonstrate the practicality of the method of this invention.

[0083] (a) Measurement of blood oxygenation using dual-band light intensity ratio:

[0084] A multispectral sensing system controls the alternating illumination of 635 nm and 980 nm LEDs, with the detector operating under corresponding bias voltages. A microprocessor records the transmitted / reflected light intensity signals I_red and I_ir for both wavelengths. By calculating the intensity ratio R = I_red / I_ir and based on a pre-calibrated curve, the module can calculate a simulated "blood oxygen saturation" value and display it in real time, demonstrating its potential application in physiological parameter monitoring.

[0085] (II) Substance Identification:

[0086] Different solutions (such as water and sucrose solution) are placed between the LED of the multispectral sensing system and the photodetector prepared by the method of this invention. Because the solutions have different absorption characteristics for different wavelengths of light, the intensity ratio of the two wavelengths measured by the multispectral sensing system will change. By establishing a database, this module can distinguish different substances, demonstrating its application in simple component analysis or concentration detection.

[0087] Example 3: Before introducing new materials or processes into practical applications, rigorous comparative experiments must be conducted to quantify their performance improvement relative to existing technologies and elucidate their underlying mechanisms. This is crucial for assessing the maturity of the technology, guiding process optimization, and persuading potential users. This example designs a comparative experiment with strictly controlled variables to demonstrate the performance of the method of this invention, providing solid data support for the reliability and superiority of the technology.

[0088] Specifically, the comparative experimental design is as follows:

[0089] 1. Design and fabrication of the control device:

[0090] In this embodiment, the intrinsic tungsten disulfide / molybdenum ditelluride device was prepared using the "single variable method": except that erbium trichloride (ErCl3) doping source was not added at all, all other materials, equipment, and process parameters were kept absolutely consistent with those in Example 1.

[0091] The erbium-doped tungsten disulfide / molybdenum ditelluride device of the present invention was prepared entirely according to the process of Example 1.

[0092] The specific preparation details are as follows:

[0093] (1) The material growth environment is the same: the same tube furnace, the same batch of tungsten trioxide and sodium chloride, the same temperature program (950℃, 10 min), the same gas atmosphere and flow rate are used to grow intrinsic monolayer tungsten disulfide on silicon dioxide / silicon substrate from the same silicon wafer.

[0094] (2) The heterostructure was constructed using the same method: nanosheets were exfoliated from the same molybdenum ditelluride crystal, and the same polydimethylsiloxane gel was used. The intrinsic tungsten disulfide / molybdenum ditelluride heterostructure was constructed on the same transfer platform with the same alignment process and heating parameters (120°C, 10 minutes) to ensure an interface area of ​​~310 μm. 2 )similar.

[0095] (3) The device fabrication methods are the same: In the same round of photolithography and coating process, the same mask, the same Cr / Au target and deposition parameters are used to prepare control devices with completely identical electrode structures.

[0096] 2. Comprehensive performance measurement and comparison from materials to devices:

[0097] (1) Intrinsic quality of the material: Raman spectroscopy shows that the erbium-doped tungsten disulfide A 1g The peak intensity was 5.5 times that of undoped tungsten disulfide, and a blue shift was observed, directly demonstrating that erbium ion doping significantly reduced lattice defects and enhanced crystal order. The 20% increase in photoluminescence intensity confirmed that non-radiative recombination channels were effectively suppressed.

[0098] (2) Electrical performance: Field effect transistor tests based on monolayer materials show that the hole mobility of erbium-doped tungsten disulfide (48 cm⁻¹) is... 2 ·V -1 ·S -1 ) is undoped tungsten disulfide (10.9 cm) 2 ·V -1 ·S -1 The scattering of carrier transport by defects is 4.4 times that of the original defects, which is 4.4 times that of the original defects.

[0099] (3) Core performance of the photodetector (at 635 nm, 0.45 mW·cm⁻¹) -2 (Under -5V conditions):

[0100] Intrinsic tungsten disulfide / molybdenum ditelluride device: photocurrent 3.45 nA, responsivity 2.59 A·W -1 Detectability 4.83×10 11 Jones, external quantum efficiency 507%.

[0101] The erbium-doped tungsten disulfide / molybdenum ditelluride device of this invention has a photocurrent of 29.4 nA and a responsivity of 20.7 A·W. -1 Specific detectivity 2.72×10 12 Jones, external quantum efficiency 4050%.

[0102] like Figure 5 and Figure 6As shown in the figure, experiments demonstrate that erbium doping leads to the following performance improvements: photocurrent increased by 8.5 times, responsivity by 8.0 times, specific detectivity by 5.6 times, and external quantum efficiency by 8.0 times. This comprehensive improvement stems from the dual effects of erbium doping: as a "defect passivator," it fills tungsten vacancies, reduces the density of trapped states, thereby improving carrier lifetime and mobility, and reducing dark current; as a "band modulator," it introduces impurity energy levels, optimizes the Type-II band shift with molybdenum ditelluride, enhances the built-in electric field, and greatly improves the separation efficiency of photogenerated carriers.

[0103] This embodiment provides indisputable data demonstrating that erbium doping is the sole key variable enabling the device to achieve a significant leap in performance. This not only elucidates the physical mechanism of the performance improvement academically, but more importantly, it proves the high added value and necessity of this doping process from an engineering application perspective. It provides a basis for investment decisions on this specific process route and demonstrates to potential users that products based on this invention will have overwhelming advantages in sensitivity, detection limit, and energy efficiency, and are expected to replace traditional solutions in the high-end optoelectronic sensing market.

[0104] 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 high-response-rate broadband van der Waals heterojunction photodetector, characterized in that, The detector, from bottom to top, includes: Supporting substrate; The erbium-doped tungsten disulfide (WS2:Er) monolayer film located on the surface of the substrate is a p-type semiconductor synthesized by in-situ chemical vapor deposition. p-type molybdenum ditelluride (MoTe2) nanosheets stacked on the erbium-doped tungsten disulfide monolayer film and forming a clean interface therewith; The erbium-doped tungsten disulfide monolayer film and the molybdenum ditelluride nanosheets are bonded by van der Waals forces to form a vertical p-type iso-heterojunction with Type-II band alignment; and Metal electrodes are formed electrically connected to the erbium-doped tungsten disulfide monolayer film and the molybdenum ditelluride nanosheets, respectively.

2. The high responsivity broadband van der Waals heterojunction photodetector according to claim 1, characterized in that, In the erbium-doped tungsten disulfide monolayer film, erbium ions (Er) 3+ It enters the tungsten disulfide lattice in a substitutional doping form, with a doping concentration of 8% to 12% atomic percentage.

3. A high-response-rate broadband van der Waals heterojunction photodetector according to claim 1 or 2, characterized in that, The metal electrode consists of an adhesion layer and a conductive layer, which are chromium / gold (Cr / Au) stacks, wherein the chromium layer has a thickness of 5 nanometers to 15 nanometers and the gold layer has a thickness of 30 nanometers to 70 nanometers.

4. A high-response-rate broadband van der Waals heterojunction photodetector according to claim 1, characterized in that, The substrate is a silicon (Si) wafer with a silicon dioxide (SiO2) insulating layer thermally grown on its surface, and the thickness of the silicon dioxide layer is 280 nanometers to 320 nanometers.

5. A method for fabricating a high-response-rate broadband van der Waals heterojunction photodetector, characterized in that, Includes the following steps: S1: Erbium-doped tungsten disulfide monolayer films are grown on silicon dioxide / silicon substrates using a dual-temperature zone tubular chemical vapor deposition method with a mixed precursor containing tungsten trioxide, sodium chloride and erbium trichloride. S2: Molybdenum ditelluride nanosheets were obtained from molybdenum ditelluride bulk material using a mechanical exfoliation method; S3: Using micro-area fixed-point dry transfer technology, the molybdenum ditelluride nanosheets are precisely transferred onto the erbium-doped tungsten disulfide monolayer film to form a vertical van der Waals heterojunction; S4: Using micro-nano fabrication technology, metal electrodes are fabricated on the heterojunction to complete the device fabrication.

6. The method for fabricating a high-response-rate broadband van der Waals heterojunction photodetector according to claim 5, characterized in that, In step S1, the growth temperature of the chemical vapor deposition is 940°C to 960°C, the growth time is 8 minutes to 12 minutes, and the growth atmosphere is a mixture of argon and hydrogen, wherein the argon content is 90% and the hydrogen content is 10%.

7. The method for fabricating a high-response-rate broadband van der Waals heterojunction photodetector according to claim 5, characterized in that, In step S3, the micro-area fixed-point dry transfer involves heat-treating the transfer interface at 115°C to 125°C for 10 to 15 minutes.

8. The method for fabricating a high-response-rate broadband van der Waals heterojunction photodetector according to claim 5, characterized in that, In step S4, the micro-nano fabrication process includes laser direct writing lithography, electron beam evaporation deposition of chromium / gold electrodes, and acetone stripping.

9. A photoelectric detection system, characterized in that, It includes at least one high-response-rate broadband van der Waals heterojunction photodetector as described in any one of claims 1-4, for use in broadband optical signal detection from the visible to the near-infrared band.

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