A van der Waals heterojunction infrared photodetector and its preparation method
Through the fully depleted van der Waals heterojunction structure and self-aligned electrode microcavity design, the limitations of existing infrared photodetectors operating at low temperatures are solved, reducing dark current and accelerating photogenerated carrier separation at room temperature, and improving light absorption efficiency and response speed.
Patent Information
- Application Number
- CN202210920365.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-08-02
- Publication Date
- 2025-07-08
- Estimated Expiration
- 2042-08-02
AI Technical Summary
Existing infrared photodetectors based on HgCdTe, PbSe and InSb materials need to operate at low temperatures to reduce dark currents and noise generated by heat, limiting their wide application, and photoconductive devices have problems with high dark currents and slow separation rates of photogenerated carriers.
A fully depleted van der Waals heterojunction structure is adopted, including a first n-type two-dimensional semiconductor layer, a p-type two-dimensional semiconductor layer and a second n-type two-dimensional semiconductor layer arranged in sequence from bottom to top, and a microcavity is formed by combining a self-aligning electrode and a bottom electrode to accelerate photogenerated carrier separation through a built-in electric field, and the potential barrier is reduced by matching the Bi-MoS2 work function.
Effectively reduce dark current at room temperature, improve light absorption efficiency and photogenerated carrier separation rate, and achieve ultra-fast response speed and high stability.
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Figure CN115274911B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of optoelectronic detection, and particularly to a van der Waals heterojunction infrared optoelectronic detector and a preparation method thereof. Background Art
[0002] Blackbody response is highly desirable for two-dimensional infrared optoelectronic detectors as it determines their practical applications. Detectors based on HgCdTe, PbSe, and InSb materials are currently the most advanced blackbody response mid-wave infrared (MWIR) detectors. However, these optoelectronic detectors must operate at low temperatures in order to reduce thermally generated dark current and noise, which not only increases the size and cost of the entire system but also limits their widespread applications. Therefore, there is an urgent need to develop the next generation of MWIR optoelectronic detectors suitable for chip-scale integration and operating at room temperature.
[0003] With the rise and development of low-dimensional materials, the discovery of two-dimensional narrow-bandgap semiconductors has brought new opportunities for uncooled MWIR detectors, and these detectors have thinner absorbers and lower noise. For example, materials such as black phosphorus (BP), Te, PdSe2, and PtSe2 have high carrier mobilities and very strong infrared light absorption. More prominently, two-dimensional layered crystals without dangling bonds can reduce generation-recombination noise and also avoid problems such as lattice mismatch. To improve the light response, researchers have proposed many new ideas and structures, such as infrared optoelectronic detectors integrating black phosphorus BP and optical waveguides, and Fabry-Perot cavities.
[0004] So far, only a few infrared optoelectronic detectors based on two-dimensional materials can be tested for blackbody response, such as photoconductive low-dimensional infrared optoelectronic detectors of black phosphorus BP, black arsenic phosphorus (BAsP), and low-dimensional Te, and photovoltaic infrared optoelectronic detectors based on the BP / MoS2 heterojunction. However, due to the Schottky barrier effect between the wide bandgap region in the photovoltaic low-dimensional infrared optoelectronic detector and the metal and the generation-recombination effect during the long-range transport of photo-generated carriers in the space charge region, its blackbody responsivity has always been difficult to exceed that of the photoconductive low-dimensional infrared optoelectronic detector. And due to the narrow bandgap characteristics of the photoconductive low-dimensional infrared detector, there is a very high dark current; in addition, the photoconductive device lacks a space charge region, the separation rate of photo-generated carriers is slow, and coupled with the significant photoconductive effect, its response speed has long restricted its application scenarios. Summary of the Invention
[0005] In view of this, the present invention provides a van der Waals heterojunction infrared optoelectronic detector and a preparation method thereof to achieve accelerating the separation of photo-generated carriers while reducing the dark current of the device.
[0006] To achieve the above object, the present invention provides the following solutions:
[0007] A van der Waals heterojunction infrared photodetector, the infrared photodetector comprising: a fully depleted van der Waals heterojunction;
[0008] The fully depleted van der Waals heterojunction includes a first n-type two-dimensional semiconductor layer, a p-type two-dimensional semiconductor layer, and a second n-type two-dimensional semiconductor layer arranged in sequence from bottom to top;
[0009] At least one side edge of the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer is in contact, and at least one side of the p-type two-dimensional semiconductor layer extends out of the gap between the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer to form an extension.
[0010] Optionally, the materials of the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer are both n-type molybdenum disulfide; the material of the p-type two-dimensional semiconductor layer is p-type black phosphorus;
[0011] The thickness of the first n-type two-dimensional semiconductor layer is 10±2nm, the thickness of the second n-type two-dimensional semiconductor layer is 20±5nm; the thickness of the p-type two-dimensional semiconductor layer is 80±5nm.
[0012] Optionally, the infrared photodetector further includes: a bottom electrode, a top electrode, a first self-aligned electrode, and a second self-aligned electrode;
[0013] The bottom electrode is arranged below the first n-type two-dimensional semiconductor layer, and the first self-aligned electrode is arranged above the second n-type two-dimensional semiconductor layer;
[0014] The top electrode is arranged above the extension of the p-type two-dimensional semiconductor layer;
[0015] The second self-aligned electrode is arranged above the top electrode and / or the extension.
[0016] Optionally, the work functions of the first self-aligned electrode and the second self-aligned electrode are used as the first work function;
[0017] The work functions of the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer are used as the second work function;
[0018] The similarity between the first work function and the second work function is greater than a preset threshold.
[0019] Optionally, both the bottom electrode and the top electrode include a Cr layer and a first Au layer arranged in sequence from bottom to top, the thickness of the Cr layer is 5-15nm, and the thickness of the first Au layer is 30-50nm;
[0020] Both the first self-aligned electrode and the second self-aligned electrode include a Bi layer and a second Au layer arranged in sequence from bottom to top. The thickness of the Bi layer is 8 ± 1 nm, and the thickness of the second Au layer is 2 ± 1 nm.
[0021] Optionally, the first self-aligned electrode and the second self-aligned electrode are formed by a self-alignment process.
[0022] Optionally, the infrared photodetector further includes: a substrate layer and an insulating layer;
[0023] The insulating layer is disposed on the upper part of the substrate layer, and the bottom electrode is disposed on the upper part of the insulating layer.
[0024] A method for fabricating a van der Waals heterojunction infrared photodetector, the fabrication method comprising the following steps:
[0025] Prepare a first n-type two-dimensional semiconductor layer and a second n-type two-dimensional semiconductor layer by mechanical exfoliation, and transfer the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer onto a glass slide coated with a polycarbonate film;
[0026] Prepare a p-type two-dimensional semiconductor layer by mechanical exfoliation, and transfer the p-type two-dimensional semiconductor layer onto a glass slide coated with a polycarbonate film;
[0027] Use the polycarbonate film to sequentially transfer the first n-type two-dimensional semiconductor layer, the p-type two-dimensional semiconductor layer, and the second n-type two-dimensional semiconductor layer onto the bottom electrode of the infrared photodetector, and make at least one side edge of the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer in contact, and make at least one side of the p-type two-dimensional semiconductor layer extend out of the gap between the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer to form an extension portion.
[0028] Optionally, the fabrication method further includes:
[0029] Fabricate a top electrode on the extension portion;
[0030] Use a self-alignment process to fabricate self-aligned electrodes on the second n-type two-dimensional semiconductor layer, the extension portion, and the top electrode, and form a first self-aligned electrode on the second n-type two-dimensional semiconductor layer, and form a second self-aligned electrode on the extension portion and / or the top electrode.
[0031] An above-mentioned fully depleted van der Waals heterojunction.
[0032] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:
[0033] The present invention discloses a van der Waals heterojunction infrared photodetector and a preparation method thereof. The infrared photodetector includes: a fully depleted van der Waals heterojunction; the fully depleted van der Waals heterojunction includes a first n-type two-dimensional semiconductor layer, a p-type two-dimensional semiconductor layer, and a second n-type two-dimensional semiconductor layer arranged in sequence from bottom to top. By forming a fully depleted built-in electric field through a sandwich structure including a first n-type two-dimensional semiconductor layer, a p-type two-dimensional semiconductor layer, and a second n-type two-dimensional semiconductor layer, the present invention realizes accelerating the separation of photo-generated carriers while reducing the dark current of the device.
[0034] Moreover, the standing wave effect generated by the microcavity formed by the bottom electrode and the first self-aligned electrode in the present invention can effectively enhance the light absorption efficiency of the device.
[0035] The Au (metal, including the bottom electrode, the top electrode, the first self-aligned electrode, and the second self-aligned electrode) - semi (semiconductor, including the first n-type two-dimensional semiconductor layer, the p-type two-dimensional semiconductor layer, and the second n-type two-dimensional semiconductor layer) contact mode of the present invention, combined with the advantages of the work function of Bi-MoS2 (wherein, the work functions of Bi and MoS2 are similar, and if they are exactly the same, the potential barrier generated by the contact between the two can be completely eliminated), significantly reduces the transport barrier of photo-generated carriers and can effectively improve the collection efficiency of photo-generated carriers.
[0036] The self-aligned process can eliminate the lateral transport mode of carriers in the detector, and the longitudinal transport in the fully depleted built-in electric field of dozens of nanometers enables the device to obtain an ultra-fast response speed; and the fully encapsulated structure can greatly improve the stability of the device. BRIEF DESCRIPTION OF THE DRAWINGS
[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.
[0038] Figure 1 It is a schematic structural diagram of a van der Waals heterojunction infrared photodetector provided by an embodiment of the present invention;
[0039] Figure 2 It is a schematic diagram of the enhancement and depletion mechanism of the infrared photodetector provided by an embodiment of the present invention; Figure 2 In (a) is a schematic diagram of the working principle of the infrared photodetector, (b) is a schematic diagram of the normalized relative spectral response under blackbody radiation and the normalized absorption of the n-p-n device with and without a metal mirror, (c) is a schematic diagram of the vertical electric potential distribution of the device under zero bias, and (d) is a distribution diagram of the built-in electric field in the vertical direction;
[0040] Figure 3 Performance simulation diagram of the infrared photodetector provided by the embodiment of the present invention; Figure 3 In (a), it is a diagram showing the variation relationship of broadband spectral photovoltaic responsivity (left axis) and specific detectivity D* (right axis) with wavelength under blackbody radiation at 1073K and 1173K. In (b), it is a schematic diagram of the rise and fall time of the device when biased at 0V under 1550nm laser irradiation. In (c), it is a schematic diagram of the normalized optical response varying with the modulation frequency when biased at 0V under 1550nm laser irradiation;
[0041] Description of reference numerals:
[0042] 1. Substrate layer; 2. Insulating layer; 3. Bottom electrode; 4-1. First n-type two-dimensional semiconductor layer; 4-2. Second n-type two-dimensional semiconductor layer; 5. p-type two-dimensional semiconductor layer; 6. Top electrode; 7-1. First self-aligned electrode; 7-2. Second self-aligned electrode. Specific implementation manners
[0043] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.
[0044] The purpose of the present invention is to provide a van der Waals heterojunction infrared photodetector and its manufacturing method to achieve reducing the dark current of the device while improving the light absorption efficiency, and accelerating the separation rate and collection efficiency of photo-generated carriers.
[0045] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.
[0046] Embodiment 1
[0047] As Figure 1 shown, Embodiment 1 of the present invention provides a van der Waals heterojunction infrared photodetector, and the infrared photodetector includes: a fully depleted van der Waals heterojunction; the fully depleted van der Waals heterojunction includes a first n-type two-dimensional semiconductor layer 4-1, a p-type two-dimensional semiconductor layer 5, and a second n-type two-dimensional semiconductor layer 4-2 arranged in sequence from bottom to top; at least one side edge of the first n-type two-dimensional semiconductor layer 4-1 and the second n-type two-dimensional semiconductor layer 4-2 is in contact, and at least one side of the p-type two-dimensional semiconductor layer 5 extends out of the gap between the first n-type two-dimensional semiconductor layer 4-1 and the second n-type two-dimensional semiconductor layer 4-2 to form an extension part.
[0048] As a specific embodiment, as Figure 1 shown, the structure of the infrared photodetector specifically includes: a substrate layer 1, an insulating layer 2 on the substrate layer 1, a bottom electrode 3 is evaporated on the insulating layer 2, and a first n-type two-dimensional semiconductor layer 4-1, a p-type two-dimensional semiconductor layer 5, and a second n-type two-dimensional semiconductor layer 4-2 are sequentially transferred on the bottom electrode 3 to form a sandwich structure. A top electrode 6 is evaporated on the uncoated area (extension) of the p-type two-dimensional semiconductor layer 5, and a first self-aligned electrode 7-1 and a second self-aligned electrode 7-2 are on the topmost layer, where:
[0049] The substrate layer 1 is a Si substrate;
[0050] The insulating layer 2 is made of SiO2 with a thickness of 280 ± 10 nm;
[0051] The bottom electrode 3 is a Cr / Au electrode, and the thicknesses of Cr and Au are 5 - 15 nm and 30 - 50 nm;
[0052] Both the first n-type two-dimensional semiconductor layer 4-1 and the second n-type two-dimensional semiconductor layer 4-2 are n-type molybdenum disulfide. The thickness of the first n-type two-dimensional semiconductor layer 4-1 is about 10 ± 2 nm, and the thickness of the second n-type two-dimensional semiconductor layer 4-2 is about 20 ± 5 nm;
[0053] The p-type two-dimensional semiconductor layer 5 is p-type black phosphorus with a thickness of 80 ± 5 nm;
[0054] The top electrode 6 is a Cr / Au electrode, and the thicknesses of Cr and Au are 5 - 15 nm and 30 - 50 nm;
[0055] The first self-aligned electrode 7-1 and the second self-aligned electrode 7-2 are Bi / Au electrodes, and the thicknesses of Bi and Au are 8 ± 1 nm and 2 ± 1 nm.
[0056] Figure 2 It is a schematic diagram of the enhancement and depletion mechanisms of the infrared photodetector provided by the embodiment of the present invention. Among them, Figure 2 in (a) is a schematic diagram of the working principle of the infrared photodetector; in (b), the curves numbered (1), (2), and (3) are respectively the normalized relative spectral response intensity curve under blackbody radiation, the normalized absorption intensity curve of the simulated n-p-n device with a metal mirror, and the normalized absorption intensity curve of the simulated n-p-n device without a metal mirror. The abscissa Wavelength is the wavelength, and the ordinate Normalized intensity is the normalized intensity; (c) is a vertical potential distribution diagram of the simulated device under zero bias; (d) is an internal electric field distribution diagram in the vertical direction, where the abscissa Electric field is the electric field and the ordinate Height is the height.
[0057] AsFigure 2 As shown in Figure 2 , the working principle of the infrared photodetector of the present invention is as follows: When light is incident on the device, after multiple reflections in the cavity (the microcavity formed by the bottom electrode and the first self-aligned electrode), the light absorption is significantly enhanced. In the fully depleted van der Waals heterojunction, electrons are transferred to the conduction band of MoS2 (molybdenum disulfide), while holes are transferred to the valence band of BP (black phosphorus). For the photovoltaic response, the photo-generated carriers quickly migrate to the MoS2 in the two opposite directions at the top and bottom under the action of the longitudinal built-in electric field of the sandwich structure n-p-n device, and then are efficiently collected by the fully wrapped metal electrodes. The photo-generated holes are migrated to the BP and are efficiently collected by the self-aligned electrode above the BP.
[0058] Figure 3 is the performance simulation diagram of the infrared photodetector of the present invention. Figure 3 In (a), it is the variation relationship diagram of the broadband spectral photovoltaic responsivity (Photoresponsivity on the left axis) and the specific detectivity D* (Detectivity on the right axis) with the wavelength under the blackbody radiation at 1073K and 1173K, and the abscissa Wavelength is the wavelength. (b) is the schematic diagram of the rise and fall time of the device when biased at 0V under the irradiation of a 1550nm laser, where the abscissa time is time and the ordinate Photocurrent is the photocurrent. (c) is the schematic diagram of the normalized optical response varying with the modulation frequency when biased at 0V under the irradiation of a 1550nm laser, where the abscissa Frequency is the frequency and the ordinate Normalizedresponse is the normalized response.
[0059] Through Figure 3 It can be seen that by forming a light absorption microcavity between the bottom electrode and the first self-aligned electrode, the quantum efficiency of the device can be enhanced. The ultra-short vertical transmission distance of dozens of nanometers of the photo-generated carriers can generate an ultra-fast photoelectric response, and at the same time, the fully depleted built-in electric field can effectively suppress the dark current of the device.
[0060] Example 2
[0061] The second embodiment of the present invention provides a preparation method for a van der Waals heterojunction infrared photodetector, and the preparation method includes the following steps:
[0062] Prepare the first n-type two-dimensional semiconductor and the second n-type two-dimensional semiconductor layer by mechanical exfoliation, and transfer the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer to a glass slide coated with a polycarbonate thin film;
[0063] Prepare the p-type two-dimensional semiconductor layer by mechanical exfoliation, and transfer the p-type two-dimensional semiconductor layer to a glass slide coated with a polycarbonate thin film;
[0064] Transfer the first n-type two-dimensional semiconductor layer, the p-type two-dimensional semiconductor layer, and the second n-type two-dimensional semiconductor layer to the bottom electrode of the infrared photodetector in sequence by using a poly(propylene carbonate) film, and make the edges of at least one side of the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer contact, and make at least one side of the p-type two-dimensional semiconductor layer extend out of the gap between the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer to form an extension part.
[0065] As a specific implementation manner, the preparation method includes the following steps:
[0066] 1) Preparation of the bottom electrode
[0067] Use electron beam lithography (EBL) technology, thermal evaporation, and lift-off process to prepare the bottom electrode 3 on a Si / SiO2 substrate (including a substrate layer 1 and an insulating layer 2), where the thickness of Cr is 5 - 15 nm and the thickness of Au is 30 - 50 nm.
[0068] 2) Preparation and transfer of n-type molybdenum disulfide flakes (the first n-type two-dimensional semiconductor layer 4-1 and the second n-type two-dimensional semiconductor layer 4-2)
[0069] In a glove box protected by nitrogen, use tape to prepare molybdenum disulfide flakes by mechanical exfoliation method, and transfer them to a glass slide coated with a poly(propylene carbonate) film.
[0070] 3) Preparation and transfer of black phosphorus flakes (p-type two-dimensional semiconductor layer 5)
[0071] In a glove box protected by nitrogen, use tape to prepare black phosphorus flakes by mechanical exfoliation method, and transfer them to a glass slide coated with a poly(propylene carbonate) film.
[0072] 4) Preparation of a fully depleted van der Waals heterojunction
[0073] In a glove box protected by nitrogen, through a microscope-assisted fixed-point transfer platform, use a poly(propylene carbonate) film to transfer molybdenum disulfide, black phosphorus, and molybdenum disulfide to the bottom electrode in sequence without damage, forming a sandwich-structured npn two-dimensional van der Waals heterojunction (i.e., a fully depleted van der Waals heterojunction).
[0074] 5) Preparation of the top electrode
[0075] Use electron beam lithography (EBL) technology, thermal evaporation, and lift-off process to prepare the top electrode 6 above the p-type black phosphorus region (extension part) not covered by MoS2, where the thickness of Cr is 5 - 15 nm and the thickness of Au is 30 - 50 nm.
[0076] 6) Preparation of a self-aligned electrode
[0077] Combined with the self-alignment process, using electron beam lithography (EBL) technology, thermal evaporation and lift-off process, self-aligned electrodes are fabricated on the top molybdenum disulfide, black phosphorus, and the top electrode on the upper end of black phosphorus. A first self-aligned electrode 7-1 is formed on the top molybdenum disulfide, and a second self-aligned electrode is formed on the black phosphorus or the top electrode on the upper end of black phosphorus, where the thickness of Bi is 8 ± 1 nm and the thickness of Au is 2 ± 1 nm. After the device fabrication is completed, a layer of PMMA photoresist is spin-coated as a protective layer.
[0078] Example 3
[0079] A fully depleted van der Waals heterojunction in Example 1.
[0080] The optical absorption microcavity standing wave effect formed between the bottom electrode and the first self-aligned electrode in the present invention can enhance the quantum efficiency of the device; moreover, the sandwich fully wrapped Au-semiconductor contact mode and the work function advantage of Bi-MoS2 significantly reduce the transport barrier of photo-generated carriers. Combined with the longitudinal short-distance transport mode of carriers, the collection efficiency of photo-generated carriers can be effectively improved; in addition, the formed sandwich structure promotes the formation of a fully depleted built-in electric field inside the device, which can greatly reduce the dark current of the device and accelerate the separation of photo-generated carriers at the same time; furthermore, the self-alignment process of the device can eliminate the lateral transport mode of carriers in the detector, and the longitudinal transport in the fully depleted built-in electric field of dozens of nanometers enables the device to obtain an ultrafast response speed. The detector of the present invention has the characteristics of high quantum efficiency, high signal-to-noise ratio, and ultrafast response.
[0081] The various embodiments in this specification are described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other.
[0082] Specific examples are used in this article to elaborate on the principles and implementation manners of the present invention. The descriptions of the above embodiments are only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, based on the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present invention.
Claims
1. A van der Waals heterojunction infrared photodetector, characterized in that, The infrared photodetector includes: a fully depleted van der Waals heterojunction; The fully depleted van der Waals heterojunction includes a first n-type two-dimensional semiconductor layer, a p-type two-dimensional semiconductor layer, and a second n-type two-dimensional semiconductor layer arranged in sequence from bottom to top; Edges on at least one side of the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer are in contact, and an extension portion is formed by extending at least one side of the p-type two-dimensional semiconductor layer out of the gap between the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer; The materials of the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer are both n-type molybdenum disulfide; the material of the p-type two-dimensional semiconductor layer is p-type black phosphorus; The thickness of the first n-type two-dimensional semiconductor layer is 10±2 nm, and the thickness of the second n-type two-dimensional semiconductor layer is 20±5 nm; the thickness of the p-type two-dimensional semiconductor layer is 80±5 nm; The infrared photodetector further includes: a bottom electrode, a top electrode, a first self-aligned electrode, and a second self-aligned electrode; The bottom electrode is disposed below the first n-type two-dimensional semiconductor layer, and the first self-aligned electrode is disposed above the second n-type two-dimensional semiconductor layer; The top electrode is disposed above the extension portion of the p-type two-dimensional semiconductor layer; The second self-aligned electrode is disposed above the top electrode and / or the extension portion.
2. The van der Waals heterojunction infrared photodetector according to claim 1, wherein The work functions of the first self-aligned electrode and the second self-aligned electrode are used as the first work function; The work functions of the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer are used as the second work function; The similarity between the first work function and the second work function is greater than a preset threshold.
3. The van der Waals heterojunction infrared photodetector according to claim 1, characterized in that, Both the bottom electrode and the top electrode include a Cr layer and a first Au layer arranged in sequence from bottom to top, the thickness of the Cr layer is 5 - 15 nm, and the thickness of the first Au layer is 30 - 50 nm; Both the first self-aligned electrode and the second self-aligned electrode include a Bi layer and a second Au layer arranged in sequence from bottom to top, the thickness of the Bi layer is 8±1 nm, and the thickness of the second Au layer is 2±1 nm.
4. The van der Waals heterojunction infrared photodetector according to claim 1, wherein The first self-aligned electrode and the second self-aligned electrode are formed by a self-aligned process.
5. The van der Waals heterojunction infrared photodetector according to claim 1, wherein The infrared photodetector further includes: a substrate layer and an insulating layer; The insulating layer is disposed above the substrate layer, and the bottom electrode is disposed above the insulating layer.
6. A method for preparing a van der Waals heterojunction infrared photodetector according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: Prepare the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer by mechanical exfoliation, and transfer the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer to a glass slide coated with a polycarbonate thin film; Prepare the p-type two-dimensional semiconductor layer by mechanical exfoliation, and transfer the p-type two-dimensional semiconductor layer to a glass slide coated with a polycarbonate thin film; Transfer the first n-type two-dimensional semiconductor layer, the p-type two-dimensional semiconductor layer, and the second n-type two-dimensional semiconductor layer to the bottom electrode of the infrared photodetector in sequence by using a poly(propylene carbonate) film, and make the edges of at least one side of the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer contact, so that at least one side of the p-type two-dimensional semiconductor layer extends out of the gap between the first n-type two-dimensional semiconductor layer and the second n-type two-dimensional semiconductor layer to form an extension portion; The preparation method further includes: Prepare a top electrode on the extension portion; Prepare self-aligned electrodes on the second n-type two-dimensional semiconductor layer, the extension portion, and the top electrode by using a self-alignment process, form a first self-aligned electrode on the second n-type two-dimensional semiconductor layer, and form a second self-aligned electrode on the extension portion and / or the top electrode.
7. A fully depleted van der Waals heterojunction in the infrared photodetector according to any one of claims 1-5.