Weel semimetal long-wave infrared detector and preparation method thereof

Abstract

The invention belongs to the technical field of infrared detection, and particularly relates to a Weel semimetal long-wave infrared detector and a preparation method thereof.The Weel semimetal long-wave infrared detector comprises a substrate, a bottom electrode, a Weel semimetal layer, a graphene transparent electrode and a top electrode, and the bottom electrode, the Weel semimetal layer, the graphene transparent electrode and the top electrode are sequentially stacked on the substrate from bottom to top; forming a vertical channel; the Weel semimetal layer is used for generating light current; and the graphene transparent electrode can collect the light current generated by the Weel semimetal layer. The problem that a conventional semiconductor long-wave infrared detector is difficult to work at the room temperature is solved, the problem that an actual light response area of an existing Weel semimetal detector is limited is solved, high-performance photoelectric detection under the room-temperature zero-bias condition is achieved, and the response area of the detector is greatly increased.

Description

Technical Field

[0001] The invention belongs to the technical field of infrared detection, and in particular to a Weyl semimetal long-wave infrared detector and a preparation method thereof. Background Art

[0002] The long-wave infrared radiation of 8-14μm is the spontaneous radiation band of targets at normal temperature and is in the atmospheric window region of the infrared spectrum. Therefore, long-wave infrared detectors in this wavelength range have important 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 problems in this band.

[0003] Currently, the commonly used long-wave infrared detection is 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-wave photons through narrow bandgap design, but because the bandgap is too narrow, the detector relies on lowering the temperature to suppress the dark current, which greatly increases the cost and space occupied by the detector, limiting the application range of the detector.

[0004] Recently, the nonlinear photoelectric response based on the enhanced Berry curvature of Weyl semimetal materials is a new technical path to achieve long-wave infrared detection [CN109870234B; CN110718603B]. The intersection of the linearly dispersed conduction band and the valence band in the Weyl semimetal band structure with broken spatial inversion symmetry is called the Weyl point. The Berry curvature near the Weyl point has a divergent characteristic, forming a large nonlinear polarizability tensor element, which can generate a strong displacement current under light excitation. At the same time, the photon energy corresponding to this transition is in the mid- and long-wave infrared band, making Weyl semimetal materials particularly capable of mid- and long-wave infrared radiation detection.

[0005] However, due to the symmetry limitations of Weyl semimetal materials, the generation of the 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 light response area of ​​the detector and limits the performance of the detector. Summary of the invention

[0006] In order to solve the problem that conventional semiconductor long-wave infrared detectors are difficult to operate at room temperature and the problem that the actual light response area of ​​existing Weyl semimetal detectors is limited, the present invention proposes a Weyl semimetal long-wave infrared detector based on a vertical channel, which realizes high-performance photoelectric detection under room temperature and zero bias conditions, and greatly increases the response area of ​​the detector.

[0007] The present invention provides the following technical solutions:

[0008] First,

[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 on the substrate from bottom to top, wherein a 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; and the graphene transparent electrode can collect the photocurrent generated by the Weyl semimetal layer.

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

[0011] Furthermore, the Weyl semimetal layer uses tungsten ditelluride nanosheets.

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

[0013] Furthermore, the material of the bottom electrode and the top electrode is gold.

[0014] Furthermore, the top electrode is grounded, and the bottom electrode is connected in series with a preamplifier, a phase-locked 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 phase-locked amplifier reads the signal amplified by the preamplifier based on the frequency of the mechanical chopper and outputs it.

[0015] Second,

[0016] The present invention provides a method for preparing a Weyl semimetal long-wave infrared detector, comprising the steps of:

[0017] A top electrode is prepared on a cleaned pure silicon wafer, HMDS is dropped on 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 on the surface of the heated pure silicon wafer containing the top electrode, and the top electrode is lifted out of the pure silicon wafer using PDMS;

[0018] Selecting a cleaned silicon / silicon dioxide substrate as a substrate for a gold bottom electrode, and preparing the bottom electrode on the cleaned substrate by a standard laser lithography process and a thermal evaporation process;

[0019] A single-layer graphene film and a tungsten ditelluride film are obtained by a mechanical stripping method. 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 serves as a graphene transparent electrode, and the tungsten ditelluride film serves as a Weyl semimetal layer. The top electrode is transferred to the graphene transparent electrode by dry transfer to form a vertical channel structure, thereby obtaining a long-wave infrared detector based on a vertical channel Weyl semimetal.

[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°C.

[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 with the existing Weyl semi-metal detector [CN109870234B; CN110718603B], the present invention uses a vertical channel structure and has the following advantages:

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

[0026] (2) Existing topological semimetal detectors are based on horizontal channels and respond to the built-in electric field in the contact area between the Weyl semimetal material and the electrode, which greatly reduces the actual light response area of ​​the detector and limits the performance of the detector. Weyl semimetal materials such as tungsten ditelluride have mirror symmetry on the horizontal plane. When the light excites the carriers near the Weyl point to generate displacement current, the displacement currents generated by the mirror-symmetrical Weyl points are in opposite directions and will cancel each other out, so that the response photocurrent cannot be observed. Only near the contact position between the electrode and the material, due to the built-in electric field caused by the Schottky barrier between the electrode and the material, the mirror symmetry is broken, so that the photocurrent can be observed. In the device structure adopted by the present invention, the direction of collecting photocurrent is the vertical direction where there is no mirror symmetry, and infrared light signal detection can be achieved in the area between the bottom electrode and the top electrode, which greatly increases the effective detection area of ​​the device. The present invention greatly increases the response area of ​​the detector by combining the graphene transparent electrode with the vertical channel.

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

[0028] 3. As a zero-bandgap material, Weyl semimetal can be excited by lasers of various wavelengths at a specific Fermi surface level, thereby exhibiting a wide-spectrum photoelectric response characteristic. In addition, the present invention can work without cooling, reducing the dependence on low-temperature systems. The present invention does not require an external bias voltage when working, avoiding the problem of dark current and reducing power consumption. Based on these characteristics, the detector designed by the present invention shows great application potential in the fields of infrared imaging, night vision equipment, etc., and is particularly conducive to achieving miniaturization and low cost of equipment. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0031] Figure 3 This is a diagram showing the power dependence of the device photocurrent response according to Example 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 numerals: 1-high-resistance silicon substrate; 2-silicon dioxide insulating layer; 3-gold bottom electrode; 4-tungsten ditelluride nanosheet; 5-single-layer graphene transparent electrode; 6-gold top electrode. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be clearly described below in conjunction with the accompanying drawings. Obviously, the described embodiments are not all embodiments of the present invention, and all other embodiments obtained by ordinary technicians in the field without making creative work are within the protection scope of the present invention.

[0035] It should be noted that the directions or positional relationships indicated by terms such as “center”, “up”, “down”, “horizontal”, “left”, “right”, “front”, “back”, “lateral” and “longitudinal” are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0036] Example 1

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

[0038] The top electrode is located above the graphene transparent electrode and covers a small area; the top electrode and the bottom electrode are used to connect to an external circuit.

[0039] The substrate comprises a high-resistance silicon substrate and a silicon dioxide insulating layer arranged on the upper surface of the high-resistance silicon substrate;

[0040] The bottom electrode is a gold bottom electrode, and the top electrode is a gold top electrode. The gold bottom electrode is used as the bottom electrode to connect with the external detection circuit to transmit the electrical signal.

[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 surface level, thereby exhibiting a wide-spectrum photoelectric response characteristic.

[0042] The graphene transparent electrode, located on top of the Weyl semimetal, allows infrared light to penetrate and act on the Weyl semimetal layer, and can efficiently collect and transmit the photocurrent generated by the Weyl semimetal.

[0043] The graphene transparent electrode and the bottom electrode channel are arranged along the stacking direction to form a vertical channel. In traditional detector design, the channel is often arranged in the horizontal direction and the current flows in the horizontal plane, while 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 in the vertical direction. The direction in which displacement current can be generated in Weyl semimetal materials such as tungsten ditelluride is the vertical direction. When the direction of the displacement current is consistent with the vertical channel direction, the displacement current can be more effectively collected through the vertical channel structure. By combining the graphene transparent electrode with the vertical channel, the graphene transparent electrode can cover the entire surface of the vertical channel, capture more light signals and convert them into electrical signals, greatly increasing 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] The bias voltage applied between the graphene transparent electrode and the bottom electrode is 0V, and the Weyl semimetal long-wave infrared detector works in photovoltaic mode, that is, in the absence of external power supply (bias voltage is 0V), it relies on the photovoltage (photovoltaic effect) generated by itself to drive current.

[0045] When long-wave infrared light shines on the detector, the Weyl semimetal absorbs photons and generates photogenerated carriers, which 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, the detection of long-wave infrared light can be achieved.

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

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

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

[0050] The data of the photocurrent generated under the irradiation of 10.6 micron wavelength incident light of different powers is shown in the figure Figure 3 (The photocurrent of the detector increases linearly with the increase of the incident light power of the laser), which facilitates the calibration of the detector responsivity to 3.9 microamperes / watt.

[0051] Figure 4 The response performance of the horizontal channel device (left) and the vertical channel device (right) are 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 spot size and position during use are much lower than those of the horizontal channel device.

[0052] The above technical features constitute the best embodiment of the present invention, which has strong adaptability and best implementation effect. Non-essential technical features can be added or reduced 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, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

[0054] Example 2

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

[0056] A top electrode is prepared on a cleaned pure silicon wafer, HMDS is dropped on 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 on the surface of the heated pure silicon wafer containing the top electrode, and the top electrode is lifted out of the pure silicon wafer using PDMS;

[0057] A cleaned silicon / silicon dioxide substrate (a high-resistance silicon substrate + a silicon dioxide insulating layer disposed on its surface) is selected as a substrate for a gold bottom electrode, and a bottom electrode is prepared on the cleaned substrate by a standard laser lithography process and a thermal evaporation process;

[0058] A single-layer graphene film and a tungsten ditelluride film are obtained by a mechanical stripping method. 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 serves as a graphene transparent electrode, and the tungsten ditelluride film serves as a Weyl semimetal layer. The top electrode is transferred to the graphene transparent electrode by dry transfer to form a vertical channel structure, thereby obtaining a long-wave infrared detector based on a vertical channel Weyl semimetal.

[0059] Specifically,

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

[0061] First, the pure silicon wafer is thoroughly cleaned;

[0062] A gold top electrode is prepared on a cleaned pure silicon wafer by a standard laser lithography process and a thermal evaporation process (a gold top electrode pattern is formed on a cleaned silicon / silicon dioxide wafer by a laser lithography process, and a layer of gold is deposited on the lithography pattern by a thermal evaporation process to form a gold top electrode);

[0063] On a pure silicon wafer with a gold top electrode, hexamethyldisilazane (HMDS) was dropped to enhance the adhesion of the subsequently spin-coated PMMA to the silicon / silicon dioxide wafer surface;

[0064] A pure silicon wafer with hexamethyldisilazane (HMDS) added dropwise was placed on a hot plate at 120°C and heated for 10 minutes, and then taken out to allow the HMDS to volatilize and evenly cover the surface of the silicon / silicon dioxide wafer;

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

[0066] Use PDMS (polydimethylsiloxane) to take out the pure silicon wafer with gold top electrode and set it aside;

[0067] 2. Preparation of gold bottom electrode:

[0068] A gold bottom electrode is prepared on a cleaned silicon / silicon dioxide substrate (a high-resistance silicon substrate + a silicon dioxide insulating layer disposed on its surface) by a standard laser lithography process and a thermal evaporation process (on a cleaned silicon / silicon dioxide substrate, a pattern of a gold bottom electrode is formed by a standard laser lithography process, and a layer of gold is deposited on the lithography pattern by a thermal evaporation process to form a gold bottom electrode);

[0069] 3. Transfer and assembly of Weyl semimetal and graphene:

[0070] A single-layer graphene film and a tungsten ditelluride film are obtained by mechanical stripping. The tungsten ditelluride film is transferred to the top of the gold bottom electrode using dry transfer technology. The single-layer graphene film is then transferred to the top of the tungsten ditelluride film. The gold top electrode is transferred to the graphene transparent electrode by dry transfer to form a vertical channel structure, thereby obtaining a long-wave infrared detector based on a vertical channel Weyl semimetal.

[0071] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A Weyl semimetal long-wave infrared detector, characterized in that: It comprises a substrate, and a bottom electrode, a Weyl semimetal layer, a graphene transparent electrode and a top electrode stacked on the substrate in sequence from bottom to top, wherein a channel between the graphene transparent electrode and the bottom electrode is along the stacking direction to form 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.

2. The Weyl semimetal long-wave infrared detector according to claim 1, characterized in that: The bias voltage applied between the graphene transparent electrode and the bottom electrode is 0V, and the Weyl semimetal long-wave infrared detector operates in a photovoltaic mode.

3. The Weyl semimetal long-wave infrared detector according to claim 1, characterized in that: The Weyl semimetal layer uses tungsten ditelluride nanosheets.

4. The Weyl semimetal long-wave infrared detector according to claim 1, characterized in that: The substrate comprises a high-resistance silicon substrate and a silicon dioxide insulating layer arranged on the upper surface of the high-resistance silicon substrate.

5. The Weyl semimetal long-wave infrared detector according to claim 1, characterized in that: The materials of the bottom electrode and the top electrode are gold.

6. The Weyl semimetal long-wave infrared detector according to claim 1, characterized in that: In the external detection circuit, the top electrode is grounded, and the bottom electrode is connected to a preamplifier, a phase-locked amplifier, and a mechanical chopper connected in series in sequence; the preamplifier amplifies the current generated by the Weyl semimetal long-wave infrared detector and converts it into a voltage signal; the phase-locked amplifier reads the signal amplified by the preamplifier based on the frequency of the mechanical chopper and outputs it.

7. A method for preparing a Weyl semimetal long-wave infrared detector, characterized in that: Includes steps: A top electrode is prepared on a cleaned pure silicon wafer, HMDS is dropped on 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 on the surface of the heated pure silicon wafer containing the top electrode, and the top electrode is lifted out of the pure silicon wafer using PDMS; Selecting a cleaned silicon / silicon dioxide substrate as a substrate for a bottom electrode, and preparing the bottom electrode on the cleaned substrate by a standard laser lithography process and a thermal evaporation process; A single-layer graphene film and a tungsten ditelluride film are obtained by a mechanical stripping method. 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 serves as a graphene transparent electrode, and the tungsten ditelluride film serves as a Weyl semimetal layer. The top electrode is transferred to the graphene transparent electrode by dry transfer to form a vertical channel structure, thereby obtaining a long-wave infrared detector based on a vertical channel Weyl semimetal.

8. The preparation method according to claim 7, characterized in that: The pure silicon wafer containing the top electrode is placed on a hot plate for heating.

9. The preparation method according to claim 7, characterized in that: The heating temperature is 120°C.

10. The preparation method according to claim 7, characterized in that: The default time is 10 minutes.

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