A weyl semimetal long-wave infrared detector and a preparation method thereof

Abstract

The application belongs to the technical field of infrared detection, and particularly relates to a Weyl semimetal long-wave infrared detector and a preparation method thereof. The Weyl semimetal long-wave infrared detector comprises a substrate, a bottom electrode, a Weyl semimetal layer, a graphene transparent electrode and a top electrode which are sequentially stacked on the substrate from bottom to top, and a channel between the electrodes is formed in a stacking direction, thereby forming a vertical channel. The Weyl semimetal layer is used for generating a photoelectric current. The graphene transparent electrode can collect the photoelectric current generated by the Weyl semimetal layer. The application solves the problem that a conventional semiconductor long-wave infrared detector is difficult to work under room temperature conditions, and the problem that the actual light response area of an existing Weyl semimetal detector is limited, thereby realizing high-performance photoelectric detection under room temperature and zero bias voltage conditions, and greatly increasing the response area of the detector.

Description

Technical Field

[0001] This invention belongs to the field of infrared detection technology, specifically a Weyl semimetal long-wave infrared detector and its preparation method. Background Technology

[0002] Long-wave infrared radiation in the 8-14 μm range is the spontaneous emission band of targets at room temperature and falls within the atmospheric window region of the infrared spectrum. Therefore, long-wave infrared detectors in this wavelength range have significant application value in astronomy, medicine, environmental monitoring, and other fields. However, the photon energy corresponding to long-wave infrared radiation is very low, and conventional semiconductor photoelectric detection methods still face challenges in this wavelength range.

[0003] Currently, commonly used long-wave infrared detectors are mainly based on materials such as mercury cadmium telluride (HgCdTe), quantum well infrared detectors (QWIPs), and type II superlattices. These materials achieve the absorption of long-wavelength photons through narrow bandgap design. However, due to the excessively narrow bandgap, the detectors rely on lowering the temperature to suppress dark current, which significantly increases the cost and space required, limiting the application range of the detectors.

[0004] Recently, nonlinear photoelectric response based on enhanced Berry curvature of Weyl semimetal materials has emerged as a new technological path for long-wave infrared detection [CN109870234B; CN110718603B]. In the spatially inverted symmetry-broken band structure of Weyl semimetals, the intersection of the linearly dispersive conduction band and valence band is called the Weyl point. The Berry curvature near the Weyl point exhibits divergent characteristics, forming a large nonlinear polarizability tensor element, which can generate a strong displacement current under photoexcitation. Simultaneously, the photon energy corresponding to this transition is in the mid-to-long-wave infrared band, making Weyl semimetal materials particularly suitable for mid-to-long-wave infrared radiation detection.

[0005] However, due to the symmetry limitation of Weyl semimetal materials, the generation of displacement current effect depends on the built-in electric field in the contact area between the Weyl semimetal material and the electrode in the detector, which greatly reduces the actual optical response area of ​​the detector and limits the performance of the detector. Summary of the Invention

[0006] To address the challenges of conventional semiconductor long-wave infrared detectors operating at room temperature and the limited optical response area of ​​existing Weyl semi-metal detectors, this invention proposes a vertical-channel-based Weyl semi-metal long-wave infrared detector that achieves high-performance photoelectric detection under room temperature and zero-bias conditions, significantly increasing the detector's response area.

[0007] This invention provides the following technical solution:

[0008] Firstly,

[0009] The present invention provides a Weyl semimetal long-wave infrared detector, comprising a substrate, and a bottom electrode, a Weyl semimetal layer, a graphene transparent electrode, and a top electrode stacked sequentially on the substrate from bottom to top. The channel between the graphene transparent electrode and the bottom electrode forms a vertical channel along the stacking direction. The Weyl semimetal layer is used to generate photocurrent. The graphene transparent electrode is capable of collecting the photocurrent generated by the Weyl semimetal layer.

[0010] Furthermore, a bias voltage of 0V is applied between the graphene transparent electrode and the bottom electrode, and the Weyl semimetal long-wave infrared detector operates in photovoltaic mode.

[0011] Furthermore, the Weyl semimetal layer is made of tungsten ditelluride nanosheets.

[0012] Furthermore, the substrate includes a high-resistivity silicon substrate and a silicon dioxide insulating layer disposed on the upper surface of the high-resistivity silicon substrate.

[0013] Furthermore, the bottom electrode and the top electrode are made of gold.

[0014] Furthermore, the top electrode is grounded, and the bottom electrode is connected in series with a preamplifier, a lock-in amplifier, and a mechanical chopper. The preamplifier amplifies the current generated by the Weyl semi-metallic long-wave infrared detector and converts it into a voltage signal. The lock-in amplifier reads the signal amplified by the preamplifier based on the frequency of the mechanical chopper and outputs it.

[0015] Secondly,

[0016] This invention provides a method for fabricating a Weyl semimetal long-wave infrared detector, comprising the following steps:

[0017] A top electrode is prepared on a cleaned pure silicon wafer. HMDS is dropped onto the pure silicon wafer containing the top electrode, and the pure silicon wafer containing the top electrode is heated for a preset time. A layer of PMMA is spin-coated onto the surface of the heated pure silicon wafer containing the top electrode, and the top electrode is removed from the pure silicon wafer using PDMS.

[0018] The cleaned silicon / silicon dioxide substrate was selected as the substrate for the gold bottom electrode. The bottom electrode was fabricated on the cleaned substrate using standard laser lithography and thermal evaporation processes.

[0019] A monolayer graphene film and a tungsten ditelluride film were obtained by mechanical exfoliation. The tungsten ditelluride film and the monolayer graphene film were then transferred sequentially to the bottom electrode by dry transfer. The monolayer graphene film served as the transparent graphene electrode, and the tungsten ditelluride film served as the Weyl half-metal layer. The top electrode was then transferred onto the transparent graphene electrode by dry transfer to form a vertical channel structure, thus obtaining a long-wave infrared detector based on a vertical channel Weyl half-metal.

[0020] Furthermore, the pure silicon wafer containing the top electrode is placed on a hot plate for heating.

[0021] Furthermore, the plate temperature is 120℃.

[0022] Furthermore, the preset time is 10 minutes.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. Compared to existing Weyl semi-metal detectors [CN109870234B; CN110718603B], this invention uses a vertical channel structure, which has the following advantages:

[0025] (1) Due to the symmetry limitation of materials, the direction in which displacement current can be generated in Weyl semimetal materials such as tungsten ditelluride is vertical. The displacement current can be collected more effectively through the vertical channel structure.

[0026] (2) Existing topological semimetal detectors are based on horizontal channels. The built-in electric field at the contact area between the Weyl semimetal material and the electrode significantly reduces the actual photoresponse area of ​​the detector, limiting its performance. Weyl semimetal materials such as tungsten distellide exhibit mirror symmetry on a horizontal plane. When photoexcites carriers near the Weyl point to generate displacement currents, the displacement currents generated at the mirror-symmetric Weyl point are in opposite directions and cancel each other out, making it impossible to observe the photocurrent. Only near the contact point between the electrode and the material, due to the built-in electric field caused by the Schottky barrier, can the mirror symmetry be broken, allowing the photocurrent to be observed. In the device structure used in this invention, the direction of photocurrent collection is a vertical direction without mirror symmetry. Infrared light signal detection can be achieved in the area between the bottom and top electrodes, significantly increasing the effective detection area of ​​the device. This invention, by combining a graphene transparent electrode with a vertical channel, significantly increases the detector's response area.

[0027] 2. Compared with semiconductor material long-wave infrared detectors, the infrared detector in this invention is based on the displacement current effect related to Berry curvature in a gapless Weyl semimetal material, which can realize long-wave infrared detection under room temperature and zero bias conditions, thus expanding the application range of the detector.

[0028] 3. As a zero-bandgap material, Weyl semimetals can be excited by lasers of various wavelengths at a specific Fermi level, thus exhibiting broadband photoelectric response characteristics. In addition, this invention can operate without cooling, reducing dependence on cryogenic systems. This invention does not require the application of an external bias voltage during operation, avoiding the problem of dark current and reducing power consumption. Based on these characteristics, the detector designed in this invention shows great application potential in fields such as infrared imaging and night vision equipment, and is particularly beneficial for achieving miniaturization and cost reduction of equipment. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the Weyl semimetal long-wave infrared detector structure according to Embodiment 1 of the present invention;

[0030] Figure 2 This is a schematic diagram of the measurement circuit of the Weyl semimetal long-wave infrared detector in Embodiment 1 of the present invention;

[0031] Figure 3 This is a power dependence graph of the photocurrent response of the device in Embodiment 1 of the present invention;

[0032] Figure 4 Comparison of scanning photocurrent spectra of the horizontal channel structure (left) and the vertical channel structure (right) of the present invention;

[0033] Figure labels: 1-High-resistivity silicon substrate; 2-Silicon dioxide insulating layer; 3-Gold bottom electrode; 4-Tungsten ditelluride nanosheet; 5-Monolayer graphene transparent electrode; 6-Gold top electrode. Detailed Implementation

[0034] The technical solution of the present invention will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are not all embodiments of the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0035] It should be noted that the terms "center", "upper", "lower", "horizontal", "left", "right", "front", "rear", "lateral", "longitudinal", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0036] Example 1

[0037] A Weyl semimetal long-wave infrared detector includes a substrate, and a bottom electrode, a Weyl semimetal layer, a graphene transparent electrode, and a top electrode stacked sequentially on the substrate from bottom to top. The channel between the graphene transparent electrode and the bottom electrode forms a vertical channel along the stacking direction.

[0038] The top electrode is positioned above the transparent graphene electrode, covering a small area; the top and bottom electrodes are used to connect to external circuits.

[0039] The substrate includes a high-resistivity silicon substrate and a silicon dioxide insulating layer disposed on the upper surface of the high-resistivity silicon substrate;

[0040] The bottom electrode is made of gold, and the top electrode is made of gold. The gold bottom electrode serves as the bottom electrode and is used to connect with the external detection circuit to transmit electrical signals.

[0041] The Weyl semimetal layer is used to generate photocurrent. As a zero-bandgap material, the Weyl semimetal can be excited by lasers of various wavelengths at a specific Fermi level, thus exhibiting broadband photoelectric response characteristics.

[0042] The graphene transparent electrode, located on top of the Weyl semimetal, allows infrared light to penetrate and act on the Weyl semimetal layer, enabling efficient collection and transmission of photocurrent generated by the Weyl semimetal.

[0043] The graphene transparent electrode and the bottom electrode channel are stacked along the direction to form a vertical channel. In traditional detector designs, channels are often arranged horizontally, with current flowing in the horizontal plane. However, the vertical channel structure means that the channel is arranged along the stacking direction (i.e., perpendicular to the traditional channel direction), and the current flows vertically. In Weyl semimetal materials such as tungsten distellide, the direction in which displacement current is generated is vertical. When the direction of displacement current is consistent with the direction of the vertical channel, the vertical channel structure can collect displacement current more effectively. By combining the graphene transparent electrode with the vertical channel, the graphene transparent electrode can cover the entire surface of the vertical channel, capturing more light signals and converting them into electrical signals, which greatly increases the response area of ​​the detector. At the same time, the high transmittance of graphene ensures that the Weyl semimetal material layer can absorb as much infrared light as possible.

[0044] A bias voltage of 0V is applied between the graphene transparent electrode and the bottom electrode. The Weyl semimetal long-wave infrared detector operates in photovoltaic mode, that is, without external power supply (bias voltage of 0V), it drives the current by relying on the photogenerated voltage (photovoltaic effect) generated by itself.

[0045] When long-wave infrared light shines on the detector, the Weyl half-metal absorbs photons and generates photogenerated carriers. These carriers are separated in the vertical channel and form a photogenerated voltage between the electrodes.

[0046] By measuring this photogenerated voltage or the corresponding photogenerated current, long-wave infrared light can be detected.

[0047] The embodiments of the present invention will now be further described with reference to the accompanying drawings and examples. This embodiment is a prototype vertical channel infrared detector with a large optical response area based on the second type of Weyl semimetal tungsten ditelluride, targeting the 10.6-micron wavelength region of the long-wave infrared spectrum.

[0048] like Figure 1 As shown, the infrared detector based on Weyl semimetal in this embodiment includes a high-resistivity silicon substrate 1, a silicon dioxide insulating layer 2, a gold bottom electrode 3, a tungsten distelluride nanosheet 4, a single-layer graphene transparent electrode 5, and a gold top electrode 6 connected in sequence. During testing, the gold top electrode 6 is grounded, and the gold bottom electrode 3 is connected to an external detection circuit.

[0049] External detection circuits such as Figure 2 As shown, it includes: a preamplifier, a lock-in amplifier, and a mechanical chopper connected together. The preamplifier amplifies the current and converts it into a voltage signal. The lock-in amplifier reads the signal amplified by the preamplifier based on the frequency of the mechanical chopper and outputs it.

[0050] The data graphs of photocurrent generated under irradiation with 10.6-micron wavelength incident light of different powers are shown below. Figure 3 (The photocurrent of the detector increases linearly with the increase of the incident laser power), which facilitates the calibration of the detector responsivity of 3.9 microamps / watt.

[0051] Figure 4 The response performance of horizontal channel (left) and vertical channel (right) devices was compared. It can be seen that the response area of ​​the vertical channel device is much larger than that of the horizontal channel device, and the direction of the response photocurrent is consistent. The requirements for the size and position of the light spot are much lower for the vertical channel device than for the horizontal channel device.

[0052] The above technical features constitute the preferred embodiment of the present invention, which has strong adaptability and optimal implementation effect. Non-essential technical features can be added or removed according to actual needs to meet the needs of different situations.

[0053] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

[0054] Example 2

[0055] The present invention provides a method for fabricating a Weyl semimetal long-wave infrared detector, comprising the following steps:

[0056] The top electrode is prepared on a cleaned pure silicon wafer. HMDS is dropped onto the pure silicon wafer containing the top electrode, and the pure silicon wafer containing the top electrode is heated for a preset time. A layer of PMMA is spin-coated onto the surface of the heated pure silicon wafer containing the top electrode, and the top electrode is removed from the pure silicon wafer using PDMS.

[0057] The cleaned silicon / silicon dioxide substrate (high-resistivity silicon substrate + silicon dioxide insulating layer on its surface) is selected as the substrate for the gold bottom electrode. The bottom electrode is fabricated on the cleaned substrate by standard laser lithography and thermal evaporation processes.

[0058] A monolayer graphene film and a tungsten ditelluride film were obtained by mechanical exfoliation. The tungsten ditelluride film and the monolayer graphene film were then transferred sequentially to the bottom electrode by dry transfer. The monolayer graphene film served as the transparent graphene electrode, and the tungsten ditelluride film served as the Weyl half-metal layer. The top electrode was then transferred onto the transparent graphene electrode by dry transfer to form a vertical channel structure, thus obtaining a long-wave infrared detector based on a vertical channel Weyl half-metal.

[0059] Specifically,

[0060] 1. Preparation and proposal of gold top electrode:

[0061] First, thoroughly clean the pure silicon wafers;

[0062] Gold top electrodes are fabricated on cleaned pure silicon wafers using standard laser lithography and thermal evaporation processes (a pattern of gold top electrodes is formed on the cleaned silicon / silicon dioxide wafer using laser lithography, and a layer of gold is deposited on the lithographic pattern using thermal evaporation to form the gold top electrodes).

[0063] Hexamethyldisilazane (HMDS) is dropped onto a pure silicon wafer containing a gold dome electrode to enhance the adhesion of the subsequent spin-coated PMMA to the silicon / silicon dioxide wafer surface.

[0064] A pure silicon wafer with hexamethyldisilazane (HMDS) added was placed on a hot plate at 120°C and heated for 10 minutes. The HMDS was then removed to allow it to evaporate and evenly cover the surface of the silicon / silicon dioxide wafer.

[0065] Next, a layer of polymethyl methacrylate (PMMA) is spin-coated onto the surface of the treated pure silicon wafer as a sacrificial layer for the subsequent peeling process;

[0066] Using PDMS (polydimethylsiloxane), the pure silicon wafer with the gold top electrode is extracted and set aside for later use;

[0067] 2. Fabrication of the gold substrate electrode:

[0068] A gold base electrode is fabricated on a cleaned silicon / silicon dioxide substrate (a high-resistivity silicon substrate with a silicon dioxide insulating layer on its surface) using standard laser lithography and thermal evaporation processes. The gold base electrode pattern is formed on the cleaned silicon / silicon dioxide substrate using standard laser lithography, and a layer of gold is deposited on the lithographic pattern using thermal evaporation to form the gold base electrode.

[0069] 3. Transfer and assembly of Weyl half-metals and graphene:

[0070] A single-layer graphene film and a tungsten ditelluride film were obtained using a mechanical exfoliation method. The tungsten ditelluride film was then transferred to the top of a gold substrate electrode using a dry transfer technique. The single-layer graphene film was then transferred to the top of the tungsten ditelluride film. The gold top electrode was then transferred onto the graphene transparent electrode using a dry transfer technique to form a vertical channel structure, resulting in a long-wave infrared detector based on a vertical channel Weyl half-metal.

[0071] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A Weyl semimetal long-wave infrared detector, comprising: The substrate and, from bottom to top, the bottom electrode, the Weyl semimetal layer, the graphene transparent electrode and the top electrode are stacked in sequence on the substrate, and a channel between the graphene transparent electrode and the bottom electrode is along the stacking direction, forming a vertical channel; the Weyl semimetal layer is used to generate photocurrent; the graphene transparent electrode can collect the photocurrent generated by the Weyl semimetal layer; the Weyl semimetal layer adopts tungsten ditelluride nanosheet.

2. The Wolframide long wave infrared detector of claim 1, wherein, The bias voltage between the graphene transparent electrode and the bottom electrode is 0V, and the Weyl semimetal long-wave infrared detector works in photovoltaic mode.

3. The Wolframide long wave infrared detector of claim 1, wherein, The substrate includes a high-resistance silicon substrate and a silicon dioxide insulating layer arranged on the upper surface of the high-resistance silicon substrate.

4. The Wolframide long wave infrared detector of claim 1, wherein, The materials of the bottom electrode and the top electrode are gold.

5. The Wolframide long wave infrared detector of claim 1, wherein, In the external detection circuit, the top electrode is grounded, and the bottom electrode is connected in series with a preamplifier, a lock-in amplifier and a mechanical chopper; the preamplifier amplifies the current generated by the Weyl semimetal long-wave infrared detector and converts it into a voltage signal; the lock-in amplifier reads the signal amplified by the preamplifier based on the frequency of the mechanical chopper and outputs.

6. A method of fabricating a Weyl semimetal long-wave infrared detector, comprising: The steps include: A top electrode is prepared on a cleaned pure silicon wafer, and after dropping HMDS on the pure silicon wafer containing the top electrode, the pure silicon wafer containing the top electrode is heated for a preset time; a layer of PMMA is spin-coated on the surface of the heated pure silicon wafer containing the top electrode, and the top electrode is lifted off from the pure silicon wafer with PDMS; A cleaned silicon / silicon dioxide substrate is selected as the substrate of the bottom electrode, and a bottom electrode is prepared on the cleaned substrate by standard laser lithography process and thermal evaporation process; A single-layer graphene film and a tungsten ditelluride film are obtained by mechanical exfoliation, and the tungsten ditelluride film and the single-layer graphene film are transferred to the top of the bottom electrode in sequence by dry transfer, the single-layer graphene film serving as the graphene transparent electrode and the tungsten ditelluride film serving as the Weyl semimetal layer, and the top electrode is transferred to the graphene transparent electrode by dry transfer, forming a vertical channel structure and obtaining a long-wave infrared detector based on a Weyl semimetal vertical channel.

7. The production method according to claim 6, wherein The pure silicon wafer containing the top electrode is heated and placed on a hot plate for heating.

8. The preparation method according to claim 6, characterized in that, The heating temperature is 120℃.

9. The preparation method according to claim 6, characterized in that, The preset time is 10 minutes.

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