Twisted stacked resonant tunneling device and preparation method thereof, phase inverter and photoelectric detector

Abstract

The invention provides a twisted stacked resonant tunneling device, which comprises a ReSe2 / h-BN / ReSe2 Van der Waals heterostructure formed in a twisted stacked mode, the ReSe2 / h-BN / ReSe2 Van der Waals heterostructure comprises a top layer ReSe2, a bottom layer ReSe2 and an h-BN layer sandwiched between the top layer ReSe2 and the bottom layer ReSe2, each layer is of a thin layered structure, the top layer ReSe2 and the bottom layer ReSe2 are made of the same anisotropic material, and the h-BN layer is made of the same anisotropic material. The top layer ReSe2 and the bottom layer ReSe2 respectively have 3-6 layer thicknesses, the top layer ReSe2 and the bottom layer ReSe2 have the same layer number or different layer numbers, the h-BN layer has 3-5 layer thicknesses, and the top layer ReSe2 rotates by a distortion angle in a range of 1.8-160 degrees relative to the bottom layer ReSe2, so that the resonant tunneling device has negative differential resistance performance. The invention also provides a preparation method of the twisted stacked resonant tunneling device, an inverter comprising the twisted stacked resonant tunneling device, and a photoelectric detector comprising the twisted stacked resonant tunneling device. The crystal lattice orientation can be adjusted by changing the distortion angle, the obvious negative differential resistance is shown, the peak-to-valley ratio is increased, and the maximum PVR value can be achieved at the distortion angle of 102 degrees.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority of the prior application 202510236194.3 filed on February 28, 2025, which is incorporated herein by reference in its entirety. Technical field

[0003] The present invention relates to the technical field of resonant tunneling in van der Waals heterostructures, and particularly relates to a twisted stacked resonant tunneling device and a preparation method thereof, an inverter including the above - mentioned twisted stacked resonant tunneling device, and a photodetector including the above - mentioned twisted stacked resonant tunneling device. Background art

[0004] Van der Waals heterostructures are layered materials assembled from individual two - dimensional material layers and can be used to fabricate various electronic devices. Resonant tunneling (RT) refers to the phenomenon that particles tunnel through a potential barrier under the conditions of energy and momentum conservation, manifested as negative differential resistance (NDR), and can be applied to fields such as steep - slope switches, oscillators, high - frequency amplifiers, multivalue logic (MVL), and low - power devices. Resonant tunneling has been widely studied in two - dimensional van der Waals heterostructures.

[0005] Traditional three - dimensional (3D) RT devices use a double - barrier quantum well structure but face challenges such as lattice mismatch, impurities, and complex sub - energy bands, which limit the improvement of the peak - to - valley ratio (PVR). In contrast, two - dimensional (2D) RT devices have several advantages in fabricating an ideal device structure, such as an atomically flat transport channel, a clean interface without covalent bonds, and the feasibility of material selection, ensuring excellent performance of RT devices. Therefore, theoretical predictions indicate that the PVR of two - dimensional resonant tunneling transistors (RTTs) is several orders of magnitude higher than that of 3D RT devices. However, the PVR in the reported 2D RTTs is still relatively low, mainly due to the high valley current caused by the tail states.

[0006] In addition, the lattice orientation plays a crucial role in determining the intrinsic properties and performance of two-dimensional twisted electronic devices. However, the twist angle is usually avoided in RTT because it may introduce momentum mismatch, which must be compensated for by phonons, photons, or plasmons. For example, the MoS2-based RTT requires precise alignment of the lattice orientation between the upper and lower layers to achieve NDR. Although NDR has been studied in twisted black phosphorus, the PVR of this device is independent of the twist angle.

[0007] In view of this, there is a need to propose a new twisted stacked resonant tunneling device and its preparation method, an inverter including the above-mentioned twisted stacked resonant tunneling device, and a photodetector including the above-mentioned twisted stacked resonant tunneling device. Summary of the Invention

[0008] In view of at least one of the above problems and defects existing in the prior art, embodiments of the present invention provide a twisted stacked resonant tunneling device and its preparation method, an inverter including the above-mentioned twisted stacked resonant tunneling device, and a photodetector including the above-mentioned twisted stacked resonant tunneling device. The twisted stacked resonant tunneling device according to the present invention includes a ReSe2 / h-BN / ReSe2 van der Waals heterostructure formed in a twisted stacked manner. By rotating the top-layer ReSe2 and the bottom-layer ReSe2 made of the same anisotropic material relative to each other by an appropriate twist angle, the lattice orientation can be adjusted, effectively adjusting the momentum conservation in the van der Waals heterostructure, demonstrating twist-angle-dependent anisotropic resonant tunneling (ART), showing obvious negative differential resistance (NDR), suppressing the valley current and increasing the peak-to-valley ratio (PVR). In particular, the maximum PVR value can be obtained at a twist angle of 102°.

[0009] On the one hand, according to an embodiment of the present invention, a twisted stacked resonant tunneling device is provided, wherein the resonant tunneling device includes a van der Waals heterostructure of ReSe2 / h-BN / ReSe2 formed in a twisted stacked manner. The van der Waals heterostructure includes a top ReSe2 layer, a bottom ReSe2 layer, and an h-BN layer sandwiched between the top ReSe2 layer and the bottom ReSe2 layer. The top ReSe2 layer, the bottom ReSe2 layer, and the h-BN layer are all thin-layered structures. Among them, the top ReSe2 layer and the bottom ReSe2 layer are made of the same anisotropic material. The top ReSe2 layer and the bottom ReSe2 layer each have a thickness of 3-6 layers, and the top ReSe2 layer and the bottom ReSe2 layer have the same number of layers or different numbers of layers. The h-BN layer has a thickness of 3-5 layers. The top ReSe2 layer is rotated by a twist angle relative to the bottom ReSe2 layer, and the twist angle is in the range of 1.8°-160°, so that the resonant tunneling device has negative differential resistance performance.

[0010] Further, in some embodiments, when the twist angle is in the range of 100°-110°, the resonant tunneling device can have a tunneling current peak-to-valley ratio greater than 3. Among them, when the twist angle is 102°, the resonant tunneling device can reach the maximum tunneling current peak-to-valley ratio of 3.2.

[0011] Further, in some embodiments, when the twist angle is in the range of 40°-60°, the resonant tunneling device can have negative differential resistance with two peaks.

[0012] On the other hand, according to an embodiment of the present invention, a method for preparing the twisted stacked resonant tunneling device is provided, wherein the twist angle in the van der Waals heterostructure of ReSe2 / h-BN / ReSe2 is formed and adjusted by stacking engineering. The preparation method includes the steps:

[0013] Step S1, the van der Waals heterostructure is made by a dry transfer method of layer-by-layer transfer from bottom to top. The dry transfer method includes the steps:

[0014] Mechanically exfoliate and transfer a ReSe2 sheet onto a silicon / silicon dioxide substrate to form the bottom ReSe2 layer with a thickness of 3-6 layers;

[0015] Mechanically exfoliate and transfer an h-BN sheet onto the bottom ReSe2 layer to form the h-BN layer as a blocking layer, and the h-BN layer has a thickness of 3-5 layers;

[0016] Mechanically exfoliate and transfer the ReSe2 sheet onto the h-BN layer to form the top ReSe2 with a thickness of 3 - 6 layers, wherein the top ReSe2 and the bottom ReSe2 are made of the same anisotropic ReSe2 sheet material, and the top ReSe2 and the bottom ReSe2 have the same number of layers or different numbers of layers. While forming the top ReSe2, rotate the top ReSe2 relative to the bottom ReSe2 by a twist angle, and the twist angle is in the range of 1.8° - 160° to form the van der Waals heterostructure;

[0017] Step S2, pattern the van der Waals heterostructure to obtain the patterned van der Waals heterostructure;

[0018] Step S3, deposit Cr and Au on the patterned van der Waals heterostructure to obtain the resonant tunneling device.

[0019] Further, in some embodiments, the step of mechanically exfoliating and transferring the h-BN sheet onto the bottom ReSe2 may include:

[0020] A polycarbonate film can be coated on polydimethylsiloxane to pick up and transfer the h-BN sheet, and then the h-BN sheet can be released onto the bottom ReSe2 at a temperature range of 160°C - 200°C;

[0021] Next, the polycarbonate film can be soaked in chloroform solvent to be removed.

[0022] Further, in some embodiments, the step of rotating the top ReSe2 relative to the bottom ReSe2 by a twist angle may include: rotating the edge of the top ReSe2 relative to the edge of the bottom ReSe2 by the twist angle.

[0023] Further, in some embodiments, in the patterning step, an electron beam lithography method can be used to pattern the electrodes of the van der Waals heterostructure.

[0024] Further, in some embodiments, the deposition step may include depositing Cr and Au by thermal evaporation in a vacuum environment.

[0025] Further, in some embodiments, the deposition step may include depositing 5 nm of Cr and 50 nm of Au in a vacuum environment of 10 -5 Pa.

[0026] According to an embodiment of the present invention, an inverter is provided. The inverter includes the described twisted stacked resonant tunneling device and a ReSe2 field-effect transistor connected in series with the resonant tunneling device. When the input voltage of the inverter changes from 0V to 60V or from 60V to 0V, the inverter can output output voltages of three different values.

[0027] According to an embodiment of the present invention, a photodetector is provided. The photodetector includes the described twisted stacked resonant tunneling device, and the photodetector can generate an adjustable photovoltaic current.

[0028] The twisted stacked resonant tunneling device provided by the embodiment of the present invention, its preparation method, an inverter including the above-mentioned twisted stacked resonant tunneling device, and a photodetector including the above-mentioned twisted stacked resonant tunneling device have at least one or a part of at least one of the following advantages:

[0029] The twisted stacked resonant tunneling device according to the present invention includes a ReSe2 / h-BN / ReSe2 van der Waals heterostructure formed in a twisted stacked manner. By rotating the top ReSe2 and the bottom ReSe2 made of the same anisotropic material relative to each other by an appropriate twist angle, the lattice orientation can be adjusted, the momentum conservation in the van der Waals heterostructure can be effectively adjusted, the anisotropic resonant tunneling (ART) dependent on the twist angle is demonstrated, obvious negative differential resistance (NDR) is exhibited, the valley current is suppressed and the peak-to-valley ratio (PVR) is increased. Particularly, at a twist angle of 102°, the maximum PVR value can be obtained;

[0030] Furthermore, the anti-bipolar transfer characteristic presented by the twisted stacked resonant tunneling device according to the present invention enables it to be applied to an inverter. Based on this, the present invention also provides an inverter including the above-mentioned twisted stacked resonant tunneling device, which has a ternary logic state;

[0031] Furthermore, the twisted stacked resonant tunneling device according to the present invention shows the characteristic that the responsivity gradually increases with the increase of the laser power, which is different from typical photodetectors, and the resonant tunneling device has an adjustable photovoltaic effect, which can be adjusted by changing the gate voltage. Based on this, the present invention also provides a photodetector including the above-mentioned twisted stacked resonant tunneling device, which can generate an adjustable photovoltaic current. Description of the Drawings

[0032] These and / or other aspects and advantages of the present invention will become apparent and be readily understood from the following description of the preferred embodiments in conjunction with the drawings, in which:

[0033] Figure 1A flow chart schematically illustrates a method for preparing a twisted stack resonant tunneling device according to an embodiment of the present invention;

[0034] Figure 2 Schematic diagrams showing energy band alignment of a ReSe2 / h-BN / ReSe2 van der Waals heterostructure at twist angles of 40° and 108° according to an example of a resonant tunneling transistor according to an embodiment of the present invention are shown respectively;

[0035] Figure 3 The negative differential resistance (NDR) characteristic in the resonant tunneling transistor example with a twist angle of 102° according to an embodiment of the present invention is shown;

[0036] Figure 4 shows a double NDR peak phenomenon in an example of a resonant tunneling transistor according to an embodiment of the present invention;

[0037] Figure 5 The NDR characteristics of the resonant tunneling transistor example according to the embodiment of the present invention at different twist angles are shown;

[0038] Figure 6 The inverse bipolar transfer characteristics of the resonant tunneling transistor example according to the embodiment of the present invention at a temperature of 10K are shown;

[0039] Figure 7 A three-valued logic inverter and an adjustable self-powered photodetector according to an example of a resonant tunneling transistor according to an embodiment of the present invention are shown;

[0040] Figure 8 The graph shows the variation of the responsivity of an example of a resonant tunneling transistor according to an embodiment of the present invention under 520 nm laser irradiation at room temperature with laser power. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further specifically described below by examples and in conjunction with the accompanying drawings. In the specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation of the present invention.

[0042] Lattice orientation plays a crucial role in determining the intrinsic properties and performance of 2D twisted electronics, and the twist angle in 2D van der Waals heterostructures can be tuned through stacking engineering. Traditionally, however, the use of twist angles is usually avoided in RTT because it may introduce momentum mismatch, which in turn destroys the resonant tunneling conditions, thus affecting the negative differential resistance (NDR) and peak-to-valley ratio (PVR), and thus often requires compensation through phonons, photons, or plasmons. In practice, however, the twist angle provides an additional degree of freedom that can be used to precisely control interlayer coupling and band alignment.

[0043] In addition to the conventional optoelectronic properties, ReSe2 also has anisotropic characteristics. In short, if measurements are carried out along different directions of ReSe2, especially along directions parallel or perpendicular to the direction of the Re atomic chain, significantly different performance data can be obtained. This property stems from the special atomic structure inside ReSe2. In the two-dimensional ReSe2 atomic crystal structure, there is a Re atomic chain arranged along a specific direction. It is precisely due to the existence of such a chain that there are significant differences in various properties deviating from the orientation of this chain, that is, anisotropy, such as differences in electron transport and optical properties.

[0044] On the other hand, hexagonal boron nitride (h-BN) is a two-dimensional material with good insulation and can be used to protect and isolate two-dimensional materials. In addition, in addition to the characteristics of ordinary two-dimensional materials, such as a planar structure, an atomically flat surface, the absence of dangling bonds and trap charges, etc., h-BN also has unique excellent mechanical, chemical, thermal stability, hyperbolic optical characteristics and phonon vibration characteristics. Therefore, it has extensive applications in the fields of nonlinear optics, ultraviolet lasers or detectors, near-field optics or imaging, and protective layer materials. In addition, h-BN can be used as a dielectric layer, tunneling layer, and protective material to form heterojunctions with other two-dimensional materials and be applied in optical devices and electronic devices.

[0045] According to an embodiment of the present invention, there is provided a twisted stacked resonant tunneling device and a method for preparing the same, an inverter including the above-mentioned twisted stacked resonant tunneling device, and a photodetector including the above-mentioned twisted stacked resonant tunneling device. The twisted stacked resonant tunneling device according to the present invention includes a ReSe2 / h-BN / ReSe2 van der Waals heterostructure formed in a twisted stacked manner. By rotating the top-layer ReSe2 and the bottom-layer ReSe2 made of the same anisotropic material relative to each other by an appropriate twist angle, it is possible to adjust the lattice orientation, effectively adjust the momentum conservation in the van der Waals heterostructure, exhibit twist angle-dependent anisotropic resonant tunneling (ART), show obvious negative differential resistance (NDR), suppress valley current and improve the peak-to-valley ratio (PVR). In particular, it can have the maximum PVR value at a twist angle of 102°.

[0046] Note that in the terms used in this article, the slash " / " represents a "and" relationship, such as ReSe2 / h-BN / ReSe2, silicon / silicon dioxide.

[0047] On the one hand, according to an embodiment of the present invention, a twisted stacked resonant tunneling device is provided, wherein the resonant tunneling device includes a van der Waals heterostructure of ReSe2 / h-BN / ReSe2 formed in a twisted stacked manner. The van der Waals heterostructure includes a top ReSe2 layer, a bottom ReSe2 layer, and an h-BN layer sandwiched between the top ReSe2 layer and the bottom ReSe2 layer. The top ReSe2 layer, the bottom ReSe2 layer, and the h-BN layer are all thin-layered structures. Among them, the top ReSe2 layer and the bottom ReSe2 layer are made of the same anisotropic material. The top ReSe2 layer and the bottom ReSe2 layer each have a thickness of 3-6 layers, and the top ReSe2 layer and the bottom ReSe2 layer have the same number of layers or different numbers of layers. The h-BN layer has a thickness of 3-5 layers. The top ReSe2 layer is rotated by a twist angle with respect to the bottom ReSe2 layer, and the twist angle is in the range of 1.8°-160°, so that the resonant tunneling device has negative differential resistance performance.

[0048] In some embodiments, the twisted stacked resonant tunneling device can be a twisted stacked resonant tunneling transistor (TS-RTT).

[0049] Further, in some embodiments, when the twist angle is in the range of 100°-110°, the resonant tunneling device can have a tunneling current peak-to-valley ratio greater than 3. When the twist angle is 102°, the resonant tunneling device can reach the maximum tunneling current peak-to-valley ratio of 3.2.

[0050] Further, in some embodiments, when the twist angle is in the range of 40°-60°, the resonant tunneling device can have negative differential resistance with two peaks.

[0051] On the other hand, according to an embodiment of the present invention, a method for preparing the resonant tunneling device is provided, wherein the twist angle in the van der Waals heterostructure of ReSe2 / h-BN / ReSe2 is adjusted by stacking engineering. The preparation method includes the steps:

[0052] Step S1, the van der Waals heterostructure is formed by a dry transfer method of layer-by-layer transfer from bottom to top. The dry transfer method includes the steps:

[0053] Mechanically exfoliate and transfer a ReSe2 sheet onto a silicon / silicon dioxide substrate to form the bottom ReSe2 layer with a thickness of 3-6 layers;

[0054] Mechanically exfoliate and transfer an h-BN sheet onto the bottom ReSe2 layer to form the h-BN layer as a barrier layer, and the h-BN layer has a thickness of 3-5 layers;

[0055] Mechanically exfoliate and transfer the ReSe2 sheet onto the h-BN layer to form the top-layer ReSe2 with a thickness of 3 - 6 layers, where the top-layer ReSe2 and the bottom-layer ReSe2 are made of the same anisotropic ReSe2 sheet material, and the top-layer ReSe2 and the bottom-layer ReSe2 have the same number of layers or different numbers of layers. While forming the top-layer ReSe2, rotate the top-layer ReSe2 relative to the bottom-layer ReSe2 by a twist angle, and the twist angle is in the range of 1.8° - 160° to form the van der Waals heterostructure;

[0056] Step S2, pattern the van der Waals heterostructure to obtain the patterned van der Waals heterostructure;

[0057] Step S3, deposit Cr and Au on the patterned van der Waals heterostructure to obtain the resonant tunneling device.

[0058] Furthermore, in some embodiments, the step of mechanically exfoliating and transferring the h-BN sheet onto the bottom-layer ReSe2 may include:

[0059] A polycarbonate film can be coated on polydimethylsiloxane to pick up and transfer the h-BN sheet, and then the h-BN sheet can be released onto the bottom-layer ReSe2 at a temperature range of 160°C - 200°C;

[0060] Next, the polycarbonate film can be soaked in chloroform solvent to be removed.

[0061] In some embodiments, the step of rotating the top-layer ReSe2 relative to the bottom-layer ReSe2 by a twist angle may include: rotating the edge of the top-layer ReSe2 relative to the edge of the bottom-layer ReSe2 by a twist angle.

[0062] Furthermore, in some embodiments, in the patterning step, an electron beam lithography method can be used to pattern the electrodes of the van der Waals heterostructure.

[0063] Furthermore, in some embodiments, the deposition step may include depositing Cr and Au by thermal evaporation in a vacuum environment.

[0064] Furthermore, in some embodiments, the deposition step may include depositing 5 nm of Cr and 50 nm of Au in a vacuum environment of 10 -5 Pa.

[0065] According to an embodiment of the present invention, an inverter is provided. The inverter includes the twisted stacked resonant tunneling device described above, and a ReSe2 field effect transistor connected in series with the resonant tunneling device. When the input voltage of the inverter changes from 0V to 60V or from 60V to 0V, the inverter can output output voltages with three different values.

[0066] According to an embodiment of the present invention, a photodetector is provided. The photodetector includes the twisted stacked resonant tunneling device described above, and the photodetector can generate an adjustable photovoltaic current.

[0067] Different from traditional two-dimensional resonant tunneling devices, the twisted stacked resonant tunneling device according to an embodiment of the present invention, such as the twisted stacked resonant tunneling transistor TS-RTT, exhibits twist angle-dependent anisotropic resonant tunneling (ART), and can have the maximum PVR value at a twist angle of 102°. Theoretical calculations show that the alignment between anisotropic energy bands generates a twist angle-dependent joint density of states (JDOS), suppressing the valley current and increasing the peak-to-valley ratio (PVR). The negative differential resistance (NDR) behavior is also significantly affected by temperature and light. In addition, double NDR peaks are observed in the TS-RTT, which is attributed to the resonant tunneling between multiple anisotropic sub-bands of ReSe2.

[0068] Examples of the resonant tunneling device according to an embodiment of the present invention will be specifically described below with reference to the accompanying drawings.

[0069] See Figure 1-2, the van der Waals heterostructure of ReSe2 / h-BN / ReSe2 can be formed and adjusted through a stacking process by means of a layer-by-layer transfer method from bottom to top. First, in step S1, a ReSe2 flake can be mechanically exfoliated using 3M Scotch tape and transferred onto a silicon / silicon dioxide (Si / SiO2) substrate, such as a Si / SiO2 substrate with a SiO2 thickness of 285 nm, to form a bottom ReSe2 with a five-layer thickness, and observed with an optical microscope such as Olympus. Then, a h-BN sheet or flake is mechanically exfoliated and transferred onto the above bottom ReSe2 as a barrier layer. A polycarbonate (PC) film is coated on polydimethylsiloxane (PDMS) for picking up the h-BN flake and releasing it at 180 °C to form a h-BN layer. Subsequently, the PC is removed by soaking in chloroform for 5 minutes. Finally, a ReSe2 flake is similarly mechanically exfoliated using 3M Scotch tape and transferred onto the h-BN layer to form a top ReSe2. The above top ReSe2 and the above bottom ReSe2 are made of the same anisotropic ReSe2 sheet material. When the top ReSe2 is rotated by a twist angle relative to the bottom ReSe2, such as 1.8°, 102°, or 160°, the edge of the top ReSe2 layer can be rotated by the corresponding twist angle relative to the edge of the bottom ReSe2 layer to ensure the twist angle between the two layers. In Figure 2 , the top ReSe2 can be denoted as t-ReSe2, and the bottom ReSe2 can be denoted as b-ReSe2. Second, in step S2, an electron beam lithography technique is used, such as by means of a Zeiss Supra 55 scanning electron microscope and a Raith ELPHY Quantum electron beam lithography pattern generator, to pattern the electrodes of the above device. Finally, in step S3, 5 nm of Cr can be deposited first and then 50 nm of Au can be deposited, for example, by thermal evaporation in a high-vacuum environment of 10 -5 Pa.

[0070] The material thickness can be measured by atomic force microscopy. Raman spectroscopy and polarization-dependent Raman spectroscopy can be characterized by a confocal micro-Raman system (WITec).

[0071] Optoelectronic measurements can be carried out using a semiconductor analyzer (Keysight B1500A) in a probe station (CRX-6.5K, Lakeshore). A laser of 520 nm can be directly introduced into the probe cavity through an optical fiber, and the light intensity can be measured by a power meter.

[0072] The calculation of electronic properties can be based on density functional theory (DFT). PAW pseudopotentials and PBE exchange-correlation functions can be used, and all calculations can be implemented in VASP.

[0073] By changing the twist angle to adjust the lattice orientation, the present invention can effectively regulate the momentum conservation in the van der Waals heterostructure, providing an additional degree of freedom for adjusting the resonance tunneling (RT) conditions. In the twisted 1T'-rhenium diselenide (1T'-ReSe2), rhenium atoms form Re chains along the a-axis, resulting in in-plane anisotropy. The used 1T'-ReSe2 is an n-type semiconductor, with the minimum of the conduction band located at the Γ point (Gamma point) and the conduction band having significant band anisotropy, resulting in an angular difference of 40° between the first and second conduction bands at the Γ point.

[0074] In the ReSe2 / h-BN / ReSe2 van der Waals heterostructure, electrons near the Γ point can maintain momentum conservation even when there is a large twist angle between the two ReSe2 layers, thus realizing resonance tunneling. At the same time, the momentum mismatch can significantly reduce the joint density of states (JDOS) in other regions outside the Γ point in momentum space, leading to a reduction in the valley current. Therefore, by precisely controlling the twist angle, the PVR can be enhanced in certain specific twisted stacked resonance tunneling transistors (TS-RTTs).

[0075] Figure 3 Shows the negative differential resistance (NDR) characteristics in a resonance tunneling transistor (RTT) with a twist angle of 102°. As shown in the figure, Figure 3 (a) is a schematic diagram of a ReSe2 / h-BN / ReSe2 twisted stacked resonance tunneling transistor (TS-RTT), where the bias voltage is applied to the bottom ReSe2 layer and resonance tunneling (RT) occurs in the overlapping region. Figure 3 (b) Schematically shows the optical image of the TS-RTT with a twist angle of 102°, where the top ReSe2 and the bottom ReSe2 are separated by four layers of h-BN. Figure 3 (c) Schematically shows the polarization-dependent Raman intensities of the top ReSe2 and the bottom ReSe2 at a Raman shift of 127 cm-1. The fitted line shows that the twist angle between the top ReSe2 and the bottom ReSe2 is approximately 102°. Figure 3 (d) Schematically shows the cross-sectional view of the transmission electron microscopy (TEM) of the TS-RTT, showing the relative lattice orientations of the top ReSe2 and the bottom ReSe2. Figure 3 (e) Schematically shows the relationship between the tunneling current and the bias voltage at different gate voltages at a temperature of 10K, clearly showing the gate voltage-dependent NDR. Figure 3 (f) Schematically shows the conductance map of the TS-RTT with a twist angle of 102° at a temperature of 10K, showing the variation trend of the NDR peak with the gate voltage. Figure 3(g) Schematically shows the summary of the PVR and NDR peak positions as a function of gate voltage at a temperature of 10 K. Figure 3 (h) Schematically shows the relationship between the tunneling current and the bias voltage at different temperatures when the gate voltage is 40 V, showing that NDR is sensitive to temperature. Figure 3 (i) Schematically shows the temperature-dependent PVR comparison between TS-RTT and undistorted RTT based on MoS2 when the gate voltage is 80 V. Figure 3 (j) Schematically shows the relationship between the tunneling current and the bias voltage under 520 nm laser irradiation at a fixed gate voltage of 40 V and a temperature of 10 K, showing the results at different laser powers.

[0076] As Figure 3 shown in a, a bias voltage is applied to the underlying ReSe2, and the back gate voltage is used to adjust the carrier density and Fermi level of the top layer ReSe2 and the bottom layer ReSe2. TS-RTT consists of two ReSe2 flakes and a four-layer h-BN flake, see the optical image in Figure 3 b. The twist angle of TS-RTT is determined to be 102° by measuring the polarization-dependent Raman spectrum of the 127 cm-1 mode, as shown in Figure 3 c. Figure 3 d shows a cross-sectional transmission electron microscope (TEM) image, indicating the existence of a twisted stacking order between the top layer ReSe2 and the bottom layer ReSe2, and the top layer ReSe2 layer consists of approximately five sheets, and the bottom layer ReSe2 layer consists of approximately four sheets.

[0077] In the TS-RTT with a twist angle of 102°, obvious negative differential resistance (NDR) is observed at different gate voltages such as 20 V, 40 V, 60 V, and 80 V, as shown in Figure 3 e. As shown in Figure 3 g, as the gate voltage increases, the positions of these NDR peaks shift towards smaller bias voltages. This trend is further manifested in the conductance map of the bias voltage and the gate voltage, as shown in Figure 3 f. It is worth noting that as the gate voltage increases, the peak-to-valley ratio (PVR) is improved, and the specific summary is shown in Figure 3 g. The NDR behavior in TS-RTT shows a strong temperature dependence, as shown in Figure 3 h, while in the RTT of the prior art, the NDR behavior has a weak dependence on temperature, for example, as shown in Figure 3 i. As shown in Figure 3 h, when the gate voltage is fixed at 60 V, the NDR peak gradually weakens and finally disappears as the temperature increases from 10 K to 300 K. In addition, the tunneling current and NDR are also affected by 520 nm laser irradiation, Figure 3j shows the results at different laser powers such as 0.6 μW, 6.1 μW, and 18.2 μW. The sensitivity of the NDR peak to temperature and light illumination indicates that the NDR behavior is related to the momentum mismatch caused by specific band alignments and twist angles. The applied bias voltage aligns the Fermi levels of the top ReSe2 conduction band with those of the bottom ReSe2 conduction band, resulting in a resonant tunneling current. As the bias voltage increases, band misalignment and momentum mismatch occur in the TS-RTT, leading to a sharp decrease in PVR.

[0078] Figure 4 (a) Schematically shows the variation of the tunneling current with the bias voltage in the TS-RTT with a twist angle of 87° at a temperature of 10 K, showing a double NDR peak. Figure 4 (b) Schematically shows the conductivity map of the TS-RTT with a twist angle of 87° at a temperature of 10 K, showing the variation of the NDR peak value with the gate voltage. Figure 4 (c) Schematically shows the variation of the tunneling current with the bias voltage at different temperatures in the TS-RTT with a twist angle of 87° at a fixed gate voltage of 80 V, showing that the second peak is more sensitive to temperature. Figure 4 (d) Schematically shows the variation of the tunneling current with the bias voltage in the TS-RTT with a twist angle of 37° at a temperature of 10 K, showing a similar double NDR peak. Figure 4 (e) Schematically shows a summary of the variation of the PVR and the position of the NDR peak with the gate voltage in the TS-RTT with a twist angle of 37° at a temperature of 10 K. Figure 4 (f) Schematically shows a schematic diagram of band alignment to explain the origin of the double NDR peak.

[0079] Based on the ART between the anisotropic conduction bands in ReSe2, multiple NDR peaks are expected to appear in the TS-RTT. The present inventors fabricated TS-RTTs with different twist angles and observed double NDR peaks. Through polarization-dependent Raman spectroscopy, the twist angles of the devices were determined to be 87° and 37°, respectively. The devices both showed two gate voltage-dependent NDR peaks (as shown in Figure 4 a and 4d) and distinguishable NDR regions (as shown in Figure 4 b and 4e). Although Figure 4 the NDR peak in c weakens with increasing temperature, it is worth noting that the decay rate of the second NDR peak is faster than that of the first NDR peak, indicating that the origins of the two peaks are different. The observed double NDR peaks can be attributed to the resonant tunneling between different conduction bands in ReSe2. According to theoretical calculations, there are multiple conduction bands at the Γ point. The second NDR peak originates from the band alignment between the first conduction band of the top layer and the second conduction band of the bottom layer, as shown in Figure 4As shown in f, where t-ReSe2 can represent the top ReSe2 layer and b-ReSe2 can represent the bottom ReSe2 layer. The dispersion relation of the energy band determines the resonance tunneling condition, making the NDR peak sensitive to temperature and light illumination changes. The broadening of the energy band and the increase in hot carriers cause the peak-to-valley ratio to gradually decrease as the temperature rises and the 520 nm laser power increases.

[0080] Figure 5 (a - d) Schematically show the relationship between the tunneling current and the bias voltage of TS-RTT with twist angles of approximately 1.8° (6a), 31° (6b), 45° (6c), and 158° (6d), respectively. Figure 5 (e) Schematically shows a summary of the twist angle on PVR, indicating that PVR is enhanced in TS-RTT with larger twist angles. The dashed line is a guiding line. Figure 5 (f) Schematically shows the relationship between the tunneling probability and the energy offset of the calculated 108° twist angle TS-RTT. Figure 5 (g) Schematically shows the relationship between the calculated PVR and the twist angle, and the result is consistent with Figure 5 the experimental results in (e).

[0081] In addition, NDR has also been observed in TS-RTT with different twist angles, including Figure 5 the cases of 1.8°, 31°, 45°, and 158° shown in a - d. It can be seen that the tunneling current of TS-RTT with a twist angle of 1.8° is the largest, which can be attributed to the maximum joint density of states with momentum conservation. Obviously, PVR strongly depends on the twist angle and reaches the maximum value at 102°, as Figure 5 shown in e, which summarizes the PVR values of TS-RTT with different twist angles. It is worth noting that when a larger twist angle is introduced, the absolute value of the tunneling current will drop by two orders of magnitude. However, the valley current drops faster than the peak current, resulting in an enhancement of PVR in TS-RTT.

[0082] To simulate the tunneling current through the h-BN layer, the inventors calculated the tunneling probability between the top and bottom ReSe2 layers in a device with a twist angle of 108°, as Figure 5 shown in f. The applied electric field drives the Fermi level to the second conduction band, resulting in the appearance of the second NDR peak. This behavior is very consistent with the double NDR peaks observed in the experimental results, as Figure 5As shown in e. Further, the inventors calculated the tunneling probability by changing the twist angle between the top and bottom ReSe2 layers. The valley current is determined by the tunneling of all conduction bands between the top and bottom ReSe2 layers. Due to the anisotropy of the ReSe2 structure, tunneling depends not only on the energy matching condition but also on the momentum matching condition caused by the twist angle. When the anisotropy angle is approximately perpendicular, the energy bands between the top and bottom ReSe2 layers can achieve the maximum momentum mismatch; when the anisotropy angle is approximately parallel, the energy bands between the top and bottom ReSe2 layers can achieve the minimum momentum mismatch. For example, when the twist angle is 108°, since the two energy bands become parallel, the valley current reaches the minimum value and the PVR reaches the maximum value, as Figure 5 shown in g, which is in good agreement with the experimental results.

[0083] Figure 6 Fig. shows the anti-bipolar transfer characteristic curve presented by an example of a resonant tunneling transistor according to an embodiment of the present invention at a temperature of 10K. It can be seen from the figure that as the gate voltage increases, the current exhibits the anti-bipolar characteristic of "increasing first, then decreasing, and then increasing again".

[0084] Based on the anti-bipolar transfer characteristic of the above-mentioned TS-RTT, as Figure 6 shown, further, the present invention provides an inverter, which includes the twisted stacked resonant tunneling device and a ReSe2 field-effect transistor connected in series with the resonant tunneling device. When the input voltage of the inverter changes from 0V to 60V or from 60V to 0V, the inverter can output three different output voltages, as Figure 7 shown in a. The above inverter can be simply referred to as a "ternary inverter".

[0085] Figure 7 (a) Schematically shows a schematic diagram of a ternary inverter composed of a TS-RTT with a twist angle of 158° and a ReSe2 field-effect transistor. Figure 7 (b) Schematically shows the relationship between the output voltage and the input voltage of the inverter, demonstrating the ternary recognition. Figure 7 (c) Schematically shows the relationship between the gain and the input voltage. Figure 7 (d) Schematically shows the power dependence of the photocurrent of a TS-RTT with a twist angle of 1.8° changing with the bias voltage. Figure 7 (e) Schematically shows the gate voltage-dependent photovoltaic current, demonstrating the tunability of the self-powered photodetector. Figure 7 (f) Schematically shows the photovoltaic current durability test under ±40V gate voltage.

[0086] Figure 7 b shows the input-output characteristics (V out versus V inrelationship). For example, when V in varies from 0 V to 60 V, V out exhibits three different states: (i) when 0 V < V in < 10 V, V out is 5 V, i.e., state "2"; (ii) when 20 V < V in < 35 V, V out is 4.5 V, i.e., state "1"; (iii) when 55 V < V in < 60 V, V out is 0 V, i.e., state "0". Figure 7 b also shows the input-output voltage equivalence table of the ternary inverter of the present invention. Figure 7 c plots the gain of the inverter at different bias voltages. Two peaks can be clearly seen, corresponding to the voltage gains from logic "2" to "1" and from "1" to "0" respectively. It is worth noting that the gain of the inverter increases with the increase of the bias voltage, indicating its potential applications in storage and computing.

[0087] In addition, the present inventors detected the photo-response and photovoltaic response of the device at a twist angle of 1.8° at room temperature. When a gate voltage of -40 V was applied, the photocurrent increased with the increase of the laser power. At P = 13.8 μW, the on-off ratio was about 10 6 , as Figure 7 shown in d, and the responsivity was 1.2 mA / W, as Figure 8 shown. It is worth noting that the twisted stacked resonant tunneling device of the present invention shows the characteristic that the responsivity gradually increases with the increase of the laser power, which is different from typical photodetectors. This is because there is an h-BN barrier in the tunneling device, making it difficult to collect photoelectrons at low light power. Only when the light power increases to a sufficient level to generate enough photoelectrons can they overcome the barrier and be collected by the source and drain electrodes of the device. In addition, the present inventors found that the resonant tunneling device has an adjustable photovoltaic effect, which can be adjusted by changing the gate voltage, as Figure 7 shown in e. The adjustable photovoltaic current was confirmed by the durability measurement under periodic light illumination with a gate voltage of ±40 V (as Figure 7 shown in f), showing its potential applications in fields such as self-powered optoelectronic devices, real-time imaging, and artificial synapses.

[0088] Figure 8 shows the variation of the responsivity with the laser power of the TS-RTT according to an embodiment of the present invention at room temperature under 520-nm laser illumination. It can be seen from the figure that the responsivity R shows a trend of increasing with the increase of the 520-nm laser power, Figure 8 and 9 groups of data are shown in. The specific (P, R) values are from Figure 8From the lower left corner to the upper right corner are as follows: (0.82, 0.54599), (1.25, 0.58307), (1.71, 0.54555), (2.11, 0.55066), (4.33, 0.60847), (6.42, 0.74588), (8.67, 0.97591), (10.98, 1.08054), (13.8, 1.18573).

[0089] In summary, the twisted stacked resonant tunneling device and its manufacturing method provided according to the embodiments of the present invention, an inverter including the above-mentioned twisted stacked resonant tunneling device, and a photodetector including the above-mentioned twisted stacked resonant tunneling device may have at least one or a part of at least one of the following advantages:

[0090] The twisted stacked resonant tunneling device according to the present invention includes a ReSe2 / h-BN / ReSe2 van der Waals heterostructure formed in a twisted stacked manner. By rotating the top ReSe2 and the bottom ReSe2 made of the same anisotropic material relative to each other by an appropriate twist angle, the lattice orientation can be adjusted, the momentum conservation in the van der Waals heterostructure can be effectively adjusted, the anisotropic resonant tunneling (ART) depending on the twist angle is demonstrated, obvious negative differential resistance (NDR) is exhibited, the valley current is suppressed and the peak-to-valley ratio (PVR) is increased. Particularly, at a twist angle of 102°, the maximum PVR value can be obtained. The enhancement of this PVR is attributed to the suppression of the valley current during the tunneling process through the unique band alignment and the reduction of the joint density of states (JDOS) at a specific twist angle of 102°, which is supported by theoretical calculations. Particularly, the twisted stacked resonant tunneling device can be a twisted stacked resonant tunneling transistor TS-RTT.

[0091] Furthermore, in addition, the NDR peak caused by resonant tunneling can be used for information storage and supports multiple logic states. The twisted stacked resonant tunneling device according to the present invention can be applied to an inverter; based on this, the present invention also provides an inverter including the above-mentioned twisted stacked resonant tunneling device, which has a ternary logic state.

[0092] Furthermore, the twisted stacked resonant tunneling device according to the present invention shows the characteristic that the responsivity gradually increases with the increase of the laser power, which is different from typical photodetectors, and this resonant tunneling device has an adjustable photovoltaic effect, which can be adjusted by changing the gate voltage; based on this, the present invention also provides a photodetector including the above-mentioned twisted stacked resonant tunneling device, which can generate an adjustable photovoltaic current.

[0093] While some embodiments of the present general inventive concept have been shown and described, those of ordinary skill in the art will understand that changes may be made in these embodiments without departing from the principles and spirit of the present general inventive concept, and the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A twisted stacked resonant tunneling device, characterized in that, It includes a van der Waals heterostructure of ReSe2 / h-BN / ReSe2 formed in a twisted stacking manner. The van der Waals heterostructure includes a top ReSe2 layer and a bottom ReSe2 layer, as well as an h-BN layer sandwiched between the top ReSe2 layer and the bottom ReSe2 layer. The top ReSe2 layer, the bottom ReSe2 layer, and the h-BN layer are all thin-layered structures. Among them, the top ReSe2 layer and the bottom ReSe2 layer are made of the same anisotropic material. Among them, the top ReSe2 layer and the bottom ReSe2 layer each have a thickness of 3-6 layers, and the top ReSe2 layer and the bottom ReSe2 layer have the same number of layers or different numbers of layers. The h-BN layer has a thickness of 3-5 layers. Among them, the top ReSe2 layer is rotated by a twist angle relative to the bottom ReSe2 layer, and the twist angle is in the range of 1.8°-160°, so that the resonant tunneling device has negative differential resistance performance.

2. The resonant tunneling device according to claim 1, wherein When the twist angle is in the range of 100°-110°, the resonant tunneling device has a tunneling current peak-to-valley ratio greater than 3. Among them, when the twist angle is 102°, the resonant tunneling device reaches the maximum tunneling current peak-to-valley ratio of 3.

2.

3. The resonant tunneling device according to claim 1, wherein When the twist angle is in the range of 40°-60°, the resonant tunneling device has negative differential resistance with two peaks.

4. A method for preparing a twisted stacked resonant tunneling device according to any one of claims 1 to 3, characterized in that, The twist angle in the van der Waals heterostructure of ReSe2 / h-BN / ReSe2 is formed and adjusted by stacking engineering. The preparation method includes the steps: Step S1, the van der Waals heterostructure is made by a dry transfer method of layer-by-layer transfer from bottom to top. Among them, the dry transfer method includes the steps: Mechanically exfoliate and transfer a ReSe2 sheet onto a silicon / silicon dioxide substrate to form the bottom ReSe2 layer with a thickness of 3-6 layers; Mechanically exfoliate and transfer an h-BN sheet onto the bottom ReSe2 layer to form the h-BN layer as a blocking layer, and the h-BN layer has a thickness of 3-5 layers; Mechanically exfoliate and transfer a ReSe2 sheet onto the h-BN layer to form the top ReSe2 layer with a thickness of 3-6 layers. Among them, the top ReSe2 layer and the bottom ReSe2 layer are made of the same anisotropic ReSe2 sheet material, and the top ReSe2 layer and the bottom ReSe2 layer have the same number of layers or different numbers of layers. While forming the top ReSe2 layer, the top ReSe2 layer is rotated by a twist angle relative to the bottom ReSe2 layer, and the twist angle is in the range of 1.8°-160°, so as to form the van der Waals heterostructure; Step S2, pattern the van der Waals heterostructure to obtain a patterned van der Waals heterostructure; Step S3, deposit Cr and Au on the patterned van der Waals heterostructure to obtain the resonant tunneling device.

5. The preparation method according to claim 4, characterized in that, The step of mechanically exfoliating and transferring the h-BN sheet onto the bottom ReSe2 layer includes: A polycarbonate film is coated on polydimethylsiloxane to pick up and transfer the h-BN sheet, and then the h-BN sheet is released onto the underlying ReSe2 in a temperature range of 160 °C - 200 °C; Next, the polycarbonate film is soaked in chloroform solvent for removal.

6. The preparation method according to claim 4, characterized in that, The rotating of the top ReSe2 relative to the bottom ReSe2 by a twist angle includes: rotating the edge of the top ReSe2 relative to the edge of the bottom ReSe2 by the twist angle.

7. The preparation method according to claim 4, characterized in that, In the patterning step, an electron beam lithography method is used to pattern the electrodes of the van der Waals heterostructure.

8. The preparation method according to claim 4, characterized in that, The deposition step includes depositing Cr and Au in a vacuum environment by thermal evaporation.

9. An inverter, characterized in that, Comprising a twisted stacked resonant tunneling device according to any one of claims 1 to 3, and a ReSe2 field effect transistor connected in series with the resonant tunneling device, when the input voltage of the inverter changes from 0V to 60V or from 60V to 0V, the inverter can output output voltages of three different values.

10. A photodetector, characterized in that, Comprising a twisted stacked resonant tunneling device according to any one of claims 1 to 3, the photodetector can generate an adjustable photovoltaic current.

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