Novel avalanche photodetector for flexible wearable device

Abstract

The invention relates to a novel avalanche photodetector for flexible wearable equipment. The novel avalanche photodetector comprises a flexible substrate insulating layer, a Schottky heterojunction device layer, a metal contact electrode layer and a top gate dielectric layer, the Schottky heterojunction device layer is composed of a two-dimensional graphene layer and a two-dimensional indium selenide semiconductor layer; the metal contact electrode layer comprises a source contact electrode layer, a drain contact electrode layer and a top gate metal electrode layer; the source contact electrode layer is connected with the two-dimensional graphene layer, and the drain contact electrode layer is connected with the two-dimensional indium selenide semiconductor layer; the Schottky heterojunction is covered with the top gate dielectric layer, and the top gate metal electrode layer is connected with the top gate dielectric layer. The flexible photoelectric detector has the advantages that the flexible material is adopted, so that the photoelectric detector is ultrathin, flexible and biocompatible, and the photoelectric property of the photoelectric detector can be kept under the condition of large-angle bending or deformation. This flexible design enables the detector to be integrated into a wearable device.

Description

Technical Field

[0001] The present invention relates to the technical field of avalanche photodetectors, and more specifically, to a novel avalanche photodetector for flexible wearable devices. Background Art

[0002] The human body is a natural infrared radiation source, but the infrared radiation characteristics of the human body are different from those of the surrounding environment. The infrared life detector uses the difference between them to separate the human target to be searched from the background in an imaging manner. The central wavelength where the infrared radiation energy of the human body is more concentrated is 9.4μm, and the infrared radiation range of human skin is 3-50μm, of which the 8-14μm wave accounts for 46% of the total human radiation energy. This wavelength is an important technical parameter for designing human infrared detectors. Thermopile is a pyroelectric infrared sensor, which is a device composed of thermocouples. It has been widely used as a temperature detection device in the fields of ear thermometers, radiation thermometers, electric ovens, food temperature detection, etc. The role of the radiation detector is mainly reflected in the measurement of high-energy, low-energy α, β, γ and X-rays. In addition, infrared avalanche photodetectors are also widely used in infrared light detection and spectral analysis. By selecting suitable photosensitive materials, wavelengths in different ranges of mid-infrared can be selectively detected and imaged.

[0003] CN201410390483.0 discloses an avalanche photodetector based on graphene / silicon dioxide / silicon and a preparation method, and specifically discloses that the avalanche photodetector includes an n-type silicon substrate, a silicon dioxide isolation layer, a silicon dioxide window, a silicon dioxide insulating layer, a top electrode, a graphene film and a bottom electrode; the avalanche photodetector of the invention can perform wide-spectrum detection, solving the problem of low response of traditional silicon-based PIN junction to ultraviolet light detection; the detector uses graphene as an active layer and a transparent electrode to eliminate the dead layer and enhance the absorption of incident light; the silicon dioxide insulating layer reduces the influence of silicon surface states and suppresses the reverse saturation current; under the action of a large reverse bias, photogenerated carriers collide with the silicon lattice to generate ionization, and obtain a very high gain. However, the prior art uses a rigid silicon substrate and a silicon dioxide gate insulating layer, which cannot be applied to flexible wearable devices; due to the use of silicon semiconductors, there is scattering from phonons and impurities in carrier transport, and the response time is limited by the electron mobility therein. Summary of the invention

[0004] The purpose of the present invention is to address the deficiencies of the prior art and propose a new avalanche photodetector for flexible wearable devices.

[0005] In the first aspect, a novel avalanche photodetector for a flexible wearable device is provided, comprising: a flexible substrate insulating layer, a Schottky heterojunction device layer, a metal contact electrode layer and a top gate dielectric layer; Among them, the Schottky heterojunction device layer is arranged on the flexible substrate insulating layer, and the Schottky heterojunction device layer is composed of a two-dimensional graphene layer and a two-dimensional indium selenide semiconductor layer; the metal contact electrode layer includes a source contact electrode layer, a drain contact electrode layer and a top gate metal electrode layer; the source contact electrode layer is connected to the two-dimensional graphene layer, and the drain contact electrode layer is connected to the two-dimensional indium selenide semiconductor layer; the top gate dielectric layer covers the Schottky heterojunction, and the top gate metal electrode layer is connected to the top gate dielectric layer.

[0006] Preferably, the top gate dielectric layer is a hexagonal boron nitride film; the two-dimensional graphene layer, the two-dimensional indium selenide semiconductor layer and the hexagonal boron nitride film are all flexible materials.

[0007] Preferably, the Schottky heterojunction device layer operates in a ballistic transport mode of electrons.

[0008] Preferably, the top gate metal electrode layer adjusts the Fermi level of the two-dimensional graphene layer by applying voltage to select the absorption band of the device.

[0009] Preferably, the two-dimensional graphene layer has a zero-gap energy band structure, which increases low-energy infrared photogenerated electrons to an energy level detectable by the device through the electron scattering effect, and breaks through the Schottky barrier into the two-dimensional indium selenide semiconductor layer through hot electrons, generating a ballistic avalanche effect and achieving carrier multiplication.

[0010] Preferably, the flexible substrate insulating layer is made of polyethylene naphthalate material.

[0011] Preferably, quantum dots are integrated between the two-dimensional graphene layer and the two-dimensional indium selenide semiconductor layer.

[0012] In a second aspect, a method for preparing a novel avalanche photodetector for a flexible wearable device as described in the first aspect is provided, comprising: Step 1, preparing a flexible substrate insulating layer, and sequentially depositing Ti / Au electrodes on the flexible substrate insulating layer by electron beam evaporation under high vacuum conditions; Step 2, spin-coating PMMA on the graphene surface as a support layer, transferring the graphene from the deionized water surface to the flexible substrate insulating layer by a chemical method, and drying for a certain period of time to remove the retained moisture; Step 3: Dissolve PMMA using hot acetone, and use a mild solvent stripper and isopropanol and deionized water to repeatedly rinse to remove residues, and finally dry in a vacuum dryer; Step 4: preparing a photolithography mask for the graphene channel by laser direct writing, and patterning the graphene and separating the channels by oxygen plasma etching technology; Step 5: growing a high-quality two-dimensional indium selenide film by chemical vapor deposition; after the growth is completed, transferring the indium selenide to the surface of the graphene layer on the insulating layer of the flexible substrate by a dry transfer technology based on polydimethylsiloxane to form a heterojunction; Step 6: deposit a hexagonal boron nitride film on the surface of the heterojunction as a top gate dielectric layer; and deposit titanium / gold in sequence on the top gate dielectric layer by electron beam evaporation to form a top gate metal electrode layer.

[0013] In a third aspect, another method for preparing a novel avalanche photodetector for a flexible wearable device as described in the first aspect is provided, comprising: Step 1, preparing a flexible substrate insulating layer, and sequentially depositing Ti / Au electrodes on the flexible substrate insulating layer by electron beam evaporation under high vacuum conditions; Step 2, spin-coating PMMA on the graphene surface as a support layer, transferring the graphene from the deionized water surface to the flexible substrate insulating layer by a chemical method, and drying for a certain period of time to remove the retained moisture; Step 3: Dissolve PMMA using hot acetone, and use a mild solvent stripper and isopropanol and deionized water to repeatedly rinse to remove residues, and finally dry in a vacuum dryer; Step 4: preparing a photolithography mask for the graphene channel by laser direct writing, and patterning the graphene and separating the channels by oxygen plasma etching technology; Step 5: Spin-coating a quantum dot solution on the surface of the graphene channel to form a thin film, and performing a ligand exchange treatment with ethanedithiol to enhance the coupling between the quantum dots and graphene, thereby completing the preparation of a flexible graphene-based electronic device; Step 6: Grow a high-quality two-dimensional indium selenide film using chemical vapor deposition. After the growth is completed, transfer the indium selenide to the surface of the graphene layer on the flexible substrate insulating layer using a dry transfer technique based on polydimethylsiloxane; Step 7: deposit a hexagonal boron nitride film on the surface of the heterojunction as a top gate dielectric layer; and deposit titanium / gold in sequence on the top gate dielectric layer by electron beam evaporation to form a top gate metal electrode layer.

[0014] Preferably, the method further includes: step 8, evaluating the performance of the detector through a photocurrent response test, and performing a bending experiment to verify the flexible stability of the device under wearable conditions.

[0015] The beneficial effects of the present invention are: 1. The present invention uses flexible materials (such as flexible substrates, hexagonal boron nitride, graphene and indium selenide) to make the photodetector ultra-thin, flexible and biocompatible, and able to maintain its photoelectric performance when bent or deformed at a large angle. This flexible design enables the detector to be integrated into wearable devices and is suitable for flexible electronic application scenarios such as smart clothing and health monitoring equipment, breaking through the limitation that traditional rigid detectors cannot be applied to flexible devices.

[0016] 2. The present invention utilizes the zero bandgap characteristics of graphene, which can absorb light in the long-wave band, especially mid-infrared light. Hot electrons break through the Schottky barrier to indium selenide, producing a ballistic avalanche effect, achieving carrier multiplication, and significantly improving the sensitivity of the photodetector. In addition, the two-dimensional Schottky heterojunction structure of graphene and indium selenide enables the detector to have a wide spectral response capability and high sensitivity, covering a wide band, and is suitable for a variety of photodetection scenarios.

[0017] 3. The present invention can adjust the Fermi level of graphene by applying voltage through the top gate metal electrode, thereby adjusting the carrier concentration in the Schottky barrier region, and realizing real-time adjustment of the photoelectric response. This adjustable band function enables the detector to selectively detect light of different wavelengths according to demand. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of a new type of avalanche photodetector for flexible wearable devices; Figure 2 Another schematic diagram of the structure of a new avalanche photodetector for flexible wearable devices; Figure 3 Schematic diagram of the assembly of chemical vapor deposition graphene and quantum dot films on a flexible substrate; Figure 4a It is a linear test diagram of the IV characteristics of the Schottky heterojunction device layer; Figure 4b It is the log test graph of IV characteristics of Schottky heterojunction device layer; Figure 5a Schematic diagram of Stokes scattering; Figure 5b Schematic diagram of anti-Stokes scattering; Figure 5c Schematic diagram of Rayleigh scattering; Figure 6a A schematic diagram of the height scan back of the graphene / InSe heterojunction region based on AFM testing; Figure 6b A schematic diagram of the amplitude scan back of the graphene / InSe heterojunction region based on AFM testing; Figure 6cA schematic diagram of phase retracement of the graphene / InSe heterojunction region based on AFM testing; Figure 6d A 3D schematic diagram of the graphene / InSe heterojunction region based on AFM testing; Figure 7a This is a diagram of the prototype device; Figure 7b This is an optical microscope characterization diagram; Explanation of the reference numerals: flexible substrate insulating layer 1, two-dimensional graphene layer 2, two-dimensional indium selenide semiconductor layer 3, top gate dielectric layer 4, source contact electrode layer 5, drain contact electrode layer 6, top gate metal electrode layer 7, quantum dots 8. DETAILED DESCRIPTION

[0019] The present invention is further described below in conjunction with embodiments. The description of the following embodiments is only used to help understand the present invention. It should be noted that for ordinary persons in the art, without departing from the principle of the present invention, the present invention can also be modified in some ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0020] Embodiment 1: Graphene’s transparency and flexibility make it a viable material for wearable sensors. This inherent physical property increases design freedom, allowing opaque and bulky readout electronics to be placed far away from the sensor, thus preserving transparency and form factor of the active sensing area. In particular, graphene photodetectors sensitized with semiconductor quantum dots have key advantages such as broadband wavelength sensitivity (300 to 2000nm) and high responsivity due to built-in photoconductive gain.

[0021] The ballistic avalanche effect refers to the rapid acceleration of electrons and holes under a strong electric field, which results in high kinetic energy. When the material size is smaller than the mean free path of electrons and holes, due to the high energy obtained by electrons and holes in a strong electric field, they can be "ballistically" transported at a very high speed in semiconductor materials, that is, without significant collision or scattering. This phenomenon is in contrast to ordinary carrier drift and diffusion, which usually involve a large number of collision and scattering processes. When high-energy electrons and holes collide with lattice atoms in semiconductors, they can excite more electron-hole pairs, thus producing an avalanche effect. This multiplication effect can significantly amplify the initial optical or electrical signal. This effect can improve the response speed, energy efficiency, sensitivity and gain of avalanche photodetectors.

[0022] Based on the characteristics of graphene and the ballistic avalanche effect, Example 1 of the present application provides a new avalanche photodetector for flexible wearable devices, which utilizes the zero band gap characteristic of graphene to absorb waves in the long-wave band; and utilizes hot electrons to break through the potential barrier into indium selenide, generating a ballistic avalanche effect to multiply the carriers, thereby solving the technical problem of high-sensitivity detection of mid-infrared light.

[0023] Specifically, Figure 1 and Figure 2 As shown, the novel avalanche photodetector for flexible wearable devices comprises: a flexible substrate insulating layer 1, a Schottky heterojunction device layer, a metal contact electrode layer and a top gate dielectric layer 4; Wherein, the Schottky heterojunction device layer is arranged on the flexible substrate insulating layer 1, and the Schottky heterojunction device layer is composed of a two-dimensional graphene layer 2 and a two-dimensional indium selenide semiconductor layer 3; the metal contact electrode layer includes a source contact electrode layer 5, a drain contact electrode layer 6 and a top gate metal electrode layer 7; the source contact electrode layer 5 is connected to the two-dimensional graphene layer 2, and the drain contact electrode layer 6 is connected to the two-dimensional indium selenide semiconductor layer 3; the top gate dielectric layer 4 covers the Schottky heterojunction, and the top gate metal electrode layer 7 is connected to the top gate dielectric layer 4. Figure 7a and Figure 7b The prototype device image and optical microscope characterization image of the new avalanche photodetector are shown respectively.

[0024] Specifically, the top gate dielectric layer 4 is a hexagonal boron nitride film; the two-dimensional graphene layer 2, the two-dimensional indium selenide semiconductor layer 3 and the hexagonal boron nitride film are all flexible materials. The flexible substrate insulating layer 1 is made of polyethylene naphthalate material to achieve a fully flexible wearable photodetector.

[0025] The Schottky barrier region formed by boron nitride / graphene / indium selenide can collect mid-infrared radiation with a central wavelength of 10μm from the human body. The Fermi level of graphene is adjusted through the top gate metal electrode layer 7, and then the carrier concentration in the Schottky barrier region is adjusted. Finally, the received photocurrent can be artificially adjusted through the gate voltage on the hexagonal boron nitride. The middle layer achieves high-sensitivity detection through the graphene hot electron effect and the gain mechanism of APD in indium selenide. Graphene is used as an absorption layer and a photosensitive layer. Due to the zero band gap of graphene, most of the light can be collected. Subsequently, hot electrons are generated, which will pass through the barrier and enter indium selenide. When a large voltage is applied, an avalanche effect occurs, which multiplies the weak signal and improves the sensitivity. The IV characteristics of the Schottky heterojunction device layer are as follows: Figure 4a and Figure 4b shown.

[0026] also, Figure 5a , Figure 5b and Figure 5cThey are the schematic diagrams of Stokes scattering, Anti-Stokes scattering and Rayleigh scattering of the device. In Stokes scattering, the molecule transitions from a lower vibrational state to a higher vibrational state, absorbing the energy of the photon, causing the wavelength of the scattered light to become longer and the wave number shift to be positive; in Anti-Stokes scattering, the molecule transitions from a higher vibrational state to a lower vibrational state, releasing energy, causing the wavelength of the scattered light to become shorter and the wave number shift to be negative; in Rayleigh scattering, the wavelength of the scattered light is the same as the incident light, the energy does not change, and the wave number shift is zero. These three forms of scattering respectively show the molecular vibration, chemical bond characteristics and the mechanism of energy exchange with photons.

[0027] Furthermore, the present application also performs an atomic force microscope (AFM) test on the graphene / indium selenide heterojunction region. Figures 6a to 6d The height retrace diagram, amplitude retrace diagram, phase retrace diagram and 3D diagram of the graphene / InSe heterojunction region based on AFM testing are shown respectively. Among them, the height retrace refers to the comparison and analysis of the consistency of the forward scan and backward scan data when recording the sample surface height signal during the scanning process. The height signal directly reflects the surface morphology characteristics of the sample and identifies the influence of environmental interference or probe drift. In addition, the height retrace can also be used to analyze the mechanical properties of soft materials or special surfaces, such as local deformation or adhesion effects. It is widely used in materials science, biological sample characterization, nanomanufacturing and other fields to ensure high accuracy and reliability of surface morphology measurement. Amplitude retrace refers to the recording and comparison of the probe amplitude signal in the forward and backward scans during the scanning process. The amplitude signal reflects the vibration change of the probe when it interacts with the sample. By analyzing the difference in retrace, information on the surface morphology, adhesion, friction and energy dissipation of the sample can be obtained. This method is widely used in materials science, biology, nanomanufacturing and other fields, which can reveal the viscoelasticity, anisotropy and directional characteristics of the sample surface, and is also used to detect imaging errors and improve the reliability and accuracy of AFM data. Phase retrace refers to the recording and comparison of the probe vibration phase signal in the forward scan (from the starting point to the end point) and the backward scan (from the end point back to the starting point) during the scanning process. The phase signal reflects the characteristics of the interaction between the probe and the sample surface, such as viscoelasticity, friction, and energy dissipation. By analyzing the phase difference between the forward and backward scans, the material properties of the sample, surface energy dissipation, asymmetric interactions, and the directional dependence of the probe-sample contact force can be revealed. The 3D schematic diagram shows the sample micromorphology obtained from the analysis data.

[0028] Embodiment 2: On the basis of Example 1, Example 2 of the present application provides another novel avalanche photodetector for a flexible wearable device, comprising: a flexible substrate insulating layer 1, a Schottky heterojunction device layer, a metal contact electrode layer, a top gate dielectric layer 4 and quantum dots 8; Among them, the flexible substrate insulating layer 1 is made of polyethylene naphthalate material; the Schottky heterojunction device layer is arranged on the flexible substrate insulating layer 1, and the Schottky heterojunction device layer is composed of a two-dimensional graphene layer 2 and a two-dimensional indium selenide semiconductor layer 3; the metal contact electrode layer includes a source contact electrode layer 5, a drain contact electrode layer 6 and a top gate metal electrode layer 7; the source contact electrode layer 5 is connected to the two-dimensional graphene layer 2, and the drain contact electrode layer 6 is connected to the two-dimensional indium selenide semiconductor layer 3; the top gate dielectric layer 4 covers the Schottky heterojunction, and the top gate metal electrode layer 7 is connected to the top gate dielectric layer 4.

[0029] The Schottky heterojunction device layer operates in the ballistic transport mode of electrons. Among them, the two-dimensional graphene layer 2 and the two-dimensional indium selenide semiconductor layer 3 have a high electron mobility, and electrons can pass through the heterojunction unimpeded, which makes it fast in response speed and can achieve high-frequency and high-speed photoelectric detection. In addition, the hot electron relaxation time in the two-dimensional graphene layer 2 is super fast, and Auger scattering will occur, which has a multiplication effect, that is, more hot electrons above the Fermi surface are generated, so that the efficiency of energy and signal conversion can be improved. In addition, the atomic-level thickness of the two-dimensional material can provide the necessary conditions for the ballistic transport of carriers. The two-dimensional graphene layer 2 has a band structure with a zero band gap. The low-energy infrared photogenerated electrons are raised to the energy height detectable by the device through the scattering effect of electrons, and the graphene hot electrons are used to break through the Schottky barrier to indium selenide, generating a ballistic avalanche to multiply the carriers. This method can further improve the sensitivity. The infrared photosensitive material used in the prior art only responds to infrared light through its intrinsic band gap size.

[0030] Furthermore, the top gate metal electrode layer 7 adjusts the Fermi level of the two-dimensional graphene layer 2 by applying voltage to select the absorption band of the device and realize adjustable band photoelectric detection. However, the infrared photosensitive material used in the prior art cannot adjust its Fermi level in real time by voltage, so it cannot adjust the Schottky barrier formed by it and the silicon substrate, so it cannot adjust the photocurrent in real time.

[0031] In addition, if Figure 3 As shown, quantum dots 8 are integrated between the two-dimensional graphene layer 2 and the two-dimensional indium selenide semiconductor layer 3. The quantum dots have the following characteristics: 1. Broad spectrum absorption and high photosensitivity: Adjustable band gap: The band structure of quantum dots is affected by particle size, and the band gap can be adjusted by controlling its size, thereby achieving absorption of light of specific wavelengths.

[0032] High absorption coefficient: Quantum dots have stronger light absorption capacity than traditional semiconductor materials, so they can effectively improve light absorption efficiency and enhance the photosensitivity of photodetectors.

[0033] 2. Enhanced charge separation and transport Generation of photogenerated electron-hole pairs: Quantum dots generate electron-hole pairs after absorbing photons, and these charges can further separate and participate in the formation of electric current.

[0034] 3. Improve response speed and sensitivity The small size of quantum dots makes the path of their electron movement shorter, thereby reducing the charge migration time and increasing the response speed of the photodetector.

[0035] High photosensitivity and low noise characteristics help to improve the sensitivity of the detector, which is particularly suitable for optical signal detection under low light intensity conditions.

[0036] 4. Multi-electron excitation effect (MEG): Under the irradiation of high-energy photons, quantum dots can excite multiple electrons through a single photon, thereby generating more photogenerated charges and further improving the photoelectric conversion efficiency.

[0037] 5. Integration of flexible and transparent electronic devices Quantum dot materials can be prepared by solution method, are suitable for deposition on flexible substrates, and can be easily integrated with transparent and flexible optoelectronic devices.

[0038] It should be noted that the parts in this embodiment that are the same or similar to those in Embodiment 1 can be referenced to each other and will not be described in detail in this application.

[0039] Embodiment 3: Based on Example 1, Example 3 of the present application provides a method for preparing a novel avalanche photodetector for a flexible wearable device, comprising: Step 1, preparing a flexible substrate insulating layer 1, and sequentially depositing Ti / Au electrodes on the flexible substrate insulating layer 1 by electron beam evaporation under high vacuum conditions; Step 2: spin-coating PMMA on the graphene surface as a support layer, transferring the graphene from the deionized water surface to the flexible substrate insulating layer 1 by a chemical method, and drying for a certain period of time to remove the retained moisture; Step 3: Dissolve PMMA using hot acetone, and use a mild solvent stripper and isopropanol and deionized water to repeatedly rinse to remove residues, and finally dry in a vacuum dryer; Step 4: preparing a photolithography mask for the graphene channel by laser direct writing, and patterning the graphene and separating the channels by oxygen plasma etching technology; Step 5: Grow a high-quality two-dimensional indium selenide (InSe) thin film using chemical vapor deposition (CVD). After the growth is completed, the indium selenide is transferred to the surface of the graphene layer on the flexible substrate insulating layer 1 by a dry transfer technique based on polydimethylsiloxane (PDMS) to form a heterojunction.

[0040] The specific steps of PDMS dry transfer are: cover the surface of the indium selenide film with a layer of PDMS film, gently peel it off to pick up the indium selenide film, and transfer it to the target substrate after precise alignment. After the transfer is completed, the indium selenide and graphene layer are fully contacted and fixed by gentle heating (50-70°C) to ensure the tightness and uniformity of the interface coupling.

[0041] Step 6: deposit a hexagonal boron nitride (h-BN) film on the heterojunction surface as the top gate dielectric layer 4; and deposit titanium / gold in sequence on the top gate dielectric layer 4 by electron beam evaporation to form a top gate metal electrode layer 7.

[0042] Specifically, the h-BN film is prepared by chemical vapor deposition, and its thickness is controlled at 10-30nm to provide excellent insulation performance and mechanical flexibility. On the h-BN film, titanium / gold (Ti / Au) are sequentially deposited by electron beam evaporation to form a top gate metal electrode.

[0043] Step 7: Evaluate the detector performance through photocurrent response test, and perform bending experiment to verify the flexible stability of the device under wearable conditions.

[0044] Specifically, the method provided in this embodiment is a preparation method corresponding to the detector provided in Example 1. Therefore, the parts in this embodiment that are the same or similar to those in Example 1 can be referenced to each other and will not be repeated in this application.

[0045] Embodiment 4: Based on Example 2, Example 4 of the present application provides another method for preparing a novel avalanche photodetector for a flexible wearable device, comprising: Step 1: prepare a flexible substrate insulating layer 1, and sequentially deposit Ti and Au thin films on the flexible substrate insulating layer 1 by electron beam evaporation under high vacuum conditions.

[0046] Specifically, on a 125 μm thick biaxially oriented PEN (polyethylene terephthalate) substrate, 2 nm Ti and 20 nm Au films were sequentially deposited by electron beam evaporation under high vacuum conditions, with Ti acting as an adhesion layer and Au providing good conductivity and chemical stability.

[0047] Step 2: Spin-coat PMMA on the graphene surface as a support layer, transfer the graphene from the deionized water surface to the flexible substrate insulating layer 1 by a chemical method, and dry for a certain period of time (such as overnight) to remove retained moisture.

[0048] Step 3: Dissolve PMMA using hot acetone and remove residues by repeated rinsing with a mild solvent stripper and isopropyl alcohol (IPA) and deionized water, and finally dry in a vacuum dryer.

[0049] Step 4: Prepare a photolithography mask for the graphene channel by laser direct writing, and pattern the graphene and separate the channels by oxygen plasma etching technology.

[0050] Step 4 also includes: verifying whether the quality and uniformity of the graphene on the flexible substrate insulating layer 1 meet the requirements through large-area Raman mapping, indicating whether the intrinsic quality is reasonable.

[0051] Step 5: Spin-coat the quantum dot solution on the graphene channel surface to form a thin film, and perform ligand exchange treatment with ethylenedithiol (EDT) to enhance the coupling between the quantum dots and graphene, such as Figure 3 As shown, the preparation of flexible graphene-based electronic devices is completed.

[0052] Step 6: Grow a high-quality two-dimensional indium selenide film by chemical vapor deposition. After the growth is completed, transfer the indium selenide to the surface of the graphene layer on the flexible substrate insulating layer 1 by a dry transfer technique based on polydimethylsiloxane.

[0053] Step 7: deposit a hexagonal boron nitride film on the surface of the heterojunction as the top gate dielectric layer 4; and deposit titanium / gold in sequence on the top gate dielectric layer 4 by electron beam evaporation to form a top gate metal electrode layer 7.

[0054] Step 8: Evaluate the detector performance through photocurrent response test, and perform bending experiment to verify the flexible stability of the device under wearable conditions.

[0055] Specifically, the method provided in this embodiment is a preparation method corresponding to the detector provided in Example 2. Therefore, the parts in this embodiment that are the same or similar to those in Example 2 can be referenced to each other and will not be repeated in this application.

Claims

1. A new avalanche photodetector for flexible wearable devices, characterized by: include: Flexible substrate insulating layer (1), Schottky heterojunction device layer, metal contact electrode layer and top gate dielectric layer (4); The Schottky heterojunction device layer is arranged on the flexible substrate insulating layer (1), and the Schottky heterojunction device layer is composed of a two-dimensional graphene layer (2) and a two-dimensional indium selenide semiconductor layer (3); the metal contact electrode layer comprises a source contact electrode layer (5), a drain contact electrode layer (6) and a top gate metal electrode layer (7); the source contact electrode layer (5) is connected to the two-dimensional graphene layer (2), and the drain contact electrode layer (6) is connected to the two-dimensional indium selenide semiconductor layer (3); the top gate dielectric layer (4) covers the Schottky heterojunction, and the top gate metal electrode layer (7) is connected to the top gate dielectric layer (4).

2. The novel avalanche photodetector for flexible wearable devices according to claim 1, characterized in that: The top gate dielectric layer (4) is a hexagonal boron nitride film; the two-dimensional graphene layer (2), the two-dimensional indium selenide semiconductor layer (3) and the hexagonal boron nitride film are all flexible materials.

3. The novel avalanche photodetector for flexible wearable devices according to claim 2, characterized in that: The Schottky heterojunction device layer operates in a ballistic transport mode of electrons.

4. The novel avalanche photodetector for flexible wearable devices according to claim 3, characterized in that: The top gate metal electrode layer (7) adjusts the Fermi energy level of the two-dimensional graphene layer (2) by applying voltage, so as to select the absorption band of the device.

5. The novel avalanche photodetector for flexible wearable devices according to claim 4, characterized in that: The two-dimensional graphene layer (2) has a zero-bandgap energy band structure, and can raise low-energy infrared photogenerated electrons to an energy level detectable by the device through the electron scattering effect, and can break through the Schottky barrier through hot electrons to the two-dimensional indium selenide semiconductor layer (3), thereby generating a ballistic avalanche effect and achieving carrier multiplication.

6. The novel avalanche photodetector for flexible wearable devices according to claim 5, characterized in that: The flexible substrate insulating layer (1) is made of polyethylene naphthalate material.

7. The novel avalanche photodetector for flexible wearable devices according to claim 6, characterized in that: Quantum dots (8) are integrated between the two-dimensional graphene layer (2) and the two-dimensional indium selenide semiconductor layer (3).

8. A method for preparing a novel avalanche photodetector for a flexible wearable device as claimed in claim 1, characterized in that: include: Step 1: preparing a flexible substrate insulating layer (1), and sequentially depositing Ti / Au electrodes on the flexible substrate insulating layer (1) by electron beam evaporation under high vacuum conditions; Step 2, spin-coating PMMA as a support layer on the graphene surface, transferring the graphene from the deionized water surface to the flexible substrate insulating layer (1) by a chemical method, and drying for a certain period of time to remove the retained moisture; Step 3: Dissolve PMMA using hot acetone, and use a mild solvent stripper and isopropanol and deionized water to repeatedly rinse to remove residues, and finally dry in a vacuum dryer; Step 4: preparing a photolithography mask for the graphene channel by laser direct writing, and patterning the graphene and separating the channels by oxygen plasma etching technology; Step 5, growing a high-quality two-dimensional indium selenide thin film by chemical vapor deposition; after the growth is completed, transferring the indium selenide to the surface of the graphene layer on the flexible substrate insulating layer (1) by a dry transfer technology based on polydimethylsiloxane to form a heterojunction; Step 6: depositing a hexagonal boron nitride film on the surface of the heterojunction as a top gate dielectric layer (4); and depositing titanium / gold in sequence on the top gate dielectric layer (4) by electron beam evaporation to form a top gate metal electrode layer (7).

9. A method for preparing a novel avalanche photodetector for a flexible wearable device as claimed in claim 7, characterized in that: include: Step 1: preparing a flexible substrate insulating layer (1), and sequentially depositing Ti / Au electrodes on the flexible substrate insulating layer (1) by electron beam evaporation under high vacuum conditions; Step 2, spin-coating PMMA as a support layer on the graphene surface, transferring the graphene from the deionized water surface to the flexible substrate insulating layer (1) by a chemical method, and drying for a certain period of time to remove the retained moisture; Step 3: Dissolve PMMA using hot acetone, and use a mild solvent stripper and isopropanol and deionized water to repeatedly rinse to remove residues, and finally dry in a vacuum dryer; Step 4: preparing a photolithography mask for the graphene channel by laser direct writing, and patterning the graphene and separating the channels by oxygen plasma etching technology; Step 5: Spin-coating a quantum dot solution on the surface of the graphene channel to form a thin film, and performing a ligand exchange treatment with ethanedithiol to enhance the coupling between the quantum dots and graphene, thereby completing the preparation of a flexible graphene-based electronic device; Step 6: growing a high-quality two-dimensional indium selenide film by chemical vapor deposition; after the growth is completed, transferring the indium selenide to the surface of the graphene layer on the flexible substrate insulating layer (1) by a dry transfer technology based on polydimethylsiloxane; Step 7: depositing a hexagonal boron nitride film on the surface of the heterojunction as a top gate dielectric layer (4); and depositing titanium / gold in sequence on the top gate dielectric layer (4) by electron beam evaporation to form a top gate metal electrode layer (7).

10. The method for preparing a novel avalanche photodetector for flexible wearable devices according to claim 9, characterized in that: It also includes: Step 8, evaluating the performance of the detector through a photocurrent response test, and performing a bending experiment to verify the flexible stability of the device under wearable conditions.

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