Nonlinear Hall terahertz rectifying device and preparation method thereof

Abstract

The invention discloses a nonlinear Hall terahertz rectifying device which comprises a substrate, an oxide layer, an absorption layer and an electrode from bottom to top. The substrate is made of intrinsic high-resistance silicon, the oxide layer is made of silicon dioxide, the absorption layer is a Weel semimetal film, and the electrode is a four-end metal electrode. The Weel semimetal thin film is a niobium iridium tellurium (NbIrTe4) thin film. A cross-shaped structure is etched on the niobium-iridium-tellurium thin film, and a four-end metal electrode is manufactured through electron beam exposure, electron beam evaporation and a stripping technology. According to the invention, a simple cross-shaped geometric structure on Weel semimetal is utilized to couple an oscillating terahertz light field radiated along the longitudinal direction, and the generation of a direct current electric signal at the transverse end is realized through a nonlinear Hall effect induced by the Bell curvature, and the process does not involve the help of any external field. According to the invention, the broadband terahertz response of 0.02-0.82 THz is realized, the power consumption is low, and integration is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz detection devices, and in particular to a nonlinear Hall terahertz rectifier device and a preparation method thereof. Background Art

[0002] The nonlinear Hall effect refers to the effect that the Hall voltage in a material does not change linearly with the electric field or current under an applied electric field or current. Normally, the Hall effect describes the transverse electric field phenomenon generated when charge carriers flow under the action of a magnetic field, while the nonlinear Hall effect refers to the fact that under nonlinear conditions, the change in this transverse electric field is no longer a linear relationship, and the longitudinal current and transverse output voltage are quadratic. The study of the nonlinear Hall effect is of great significance for understanding the electronic transport properties of materials and developing new electronic devices. In practical applications, the nonlinear Hall effect is widely used in terahertz rectification, microwave frequency doubling, and energy harvesting. By studying the nonlinear Hall effect, the microscopic electronic structure and transport characteristics of the material can be revealed, providing a theoretical basis for the design of new functional materials and devices.

[0003] However, there are some key challenges to overcome in the current research on the nonlinear Hall effect. First, experiments usually need to be carried out under extremely low temperature conditions, which limits the feasibility and practicality of the effect at room temperature in practical applications. Secondly, although the nonlinear Hall effect has been observed, it has only been applied to low-frequency (<10GHz) electromagnetic wave rectification internationally. In addition, in view of the huge application demand and long-standing technical bottlenecks of existing long-wave infrared photoelectric detection technology, a new mechanism of high-speed photoinduced charge separation is achieved by manipulating electronic states based on a system of low-dimensional quantum photoelectric materials, which effectively suppresses the generation of dark current. This breaks through the constraints of the charge transport characteristics of traditional devices on cutoff frequency or wavelength, and is expected to produce a full-band Hall rectifier. Summary of the invention

[0004] The purpose of the present invention is to provide a nonlinear Hall terahertz rectifier device and a preparation method thereof, which realizes the wide-spectrum rectification application of the nonlinear Hall rectifier device of niobium, iridium and tellurium materials in the room temperature terahertz band without external field by means of the mechanism of nonlinear Hall effect. In order to achieve the above purpose, the present invention is implemented by the following technical solutions:

[0005] A nonlinear Hall terahertz rectifier device comprises a substrate, an oxide layer, an absorption layer and an electrode from bottom to top; the substrate is made of intrinsic high-resistance silicon, the oxide layer is made of silicon dioxide, the absorption layer is a Weyl semimetal film, and the electrode is a four-terminal metal electrode.

[0006] The Weyl semimetal film is a niobium iridium telluride (NbIrTe4) film.

[0007] The thickness of niobium iridium telluride (NbIrTe4) film is 15-100nm.

[0008] The resistivity of the substrate is 10000-20000Ω·cm, the thickness is 200-600μm; the thickness of the oxide layer is 200-500nm.

[0009] The resistivity of the substrate is 20000Ω·cm, the thickness is 500μm; the thickness of the oxide layer is 300nm.

[0010] The four-terminal metal electrode is a composite metal electrode divided into an upper layer and a lower layer. The upper layer metal is gold with a thickness of 45-100 nm, and the lower layer metal is chromium with a thickness of 5-25 nm.

[0011] The thickness of gold is 75nm and the thickness of chromium is 15nm.

[0012] The method for preparing the nonlinear Hall terahertz rectifier device as described above comprises the following steps:

[0013] Step 1, preparing niobium iridium telluride (NbIrTe4) single crystal by flux method;

[0014] Step 2: Mechanically exfoliate the niobium iridium telluride (NbIrTe4) single crystal to prepare a niobium iridium telluride (NbIrTe4) thin film with a thickness of 15-100 nm;

[0015] Step 3: transferring a niobium iridium telluride (NbIrTe4) thin film onto the surface of the oxide layer to form an absorption layer;

[0016] Step 4: using a focused ion beam etching method, a cross shape is etched on the absorption layer made of niobium iridium telluride (NbIrTe4) thin film;

[0017] Step 5: Apply photoresist on the cross shape etched on the absorption layer, and then use electron beam exposure, electron beam evaporation and stripping processes in sequence to make a four-terminal metal electrode, thereby completing the production of a nonlinear terahertz Hall device;

[0018] Step 6: Place the nonlinear terahertz Hall device made in step 5 on a PCB base, bond wires, and make a nonlinear terahertz Hall rectifier device.

[0019] After step six, a detection step is also included, and the detection step is:

[0020] Step 7, using a low-frequency phase-locked amplification method on the nonlinear terahertz Hall rectifier device prepared in step 6, experimentally observing the generation of a nonlinear Hall effect in a niobium iridium telluride (NbIrTe4) thin film at room temperature;

[0021] Step 8: Based on step 7, a high-frequency terahertz wave rectification experiment is performed, a linear terahertz wave is applied along the longitudinal direction of the device, and a direct current signal is collected in the transverse direction of the device.

[0022] The beneficial effects of the present invention are:

[0023] 1. As the substrate material, intrinsic high-resistance silicon has a high resistivity that can effectively reduce the scattering of terahertz light by the substrate; 2. Weyl semimetal niobium iridium telluride (NbIrTe4) is a non-centrosymmetric quantum material. One of the key characteristics of non-centrosymmetric quantum materials is the breaking of inversion symmetry, which leads to the appearance of non-zero Berry curvature in momentum space. Therefore, the integration in the Brillouin zone produces a net Berry curvature dipole, thereby inducing the nonlinear Hall effect. This effect is used to generate a strong nonlinear output signal, which can be applied to frequency doubling, high-frequency electromagnetic wave collection and wireless detection through rectification; 3. In order to ensure the accuracy of the nonlinear Hall effect test, the Weyl semimetal film is etched into a cross geometric structure using the focused ion beam etching method, which largely eliminates the contact false potential difference such as thermoelectric error, which affects the measurement of the nonlinear Hall voltage; 4. Using the non-centrosymmetric quantum material with a huge Berry curvature dipole, the room temperature nonlinear Hall effect of niobium iridium telluride (NbIrTe4) was experimentally observed for the first time; 5. At the same time, using a simple cross geometric structure, the oscillating terahertz light field radiated along the longitudinal direction can also be coupled, and the nonlinear Hall effect induced by the Berry curvature is used to achieve the generation of a direct current signal at the lateral end. This process does not involve any external field assistance, thereby realizing room temperature wide-spectrum terahertz optical rectification without an external field, with a band range of 0.02-0.82THz, improving the signal-to-noise ratio, and achieving high-sensitivity detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the cross-sectional structure of the nonlinear Hall terahertz rectifier device of the present invention.

[0025] Figure 2 It is a top view of the structure of the nonlinear Hall terahertz rectifier device of the present invention.

[0026] Figure 3 It is a schematic diagram of testing the nonlinear Hall effect of the nonlinear Hall terahertz rectifier of the present invention.

[0027] Figure 4 is the horizontal and vertical fundamental frequency V ω , frequency multiplier V 2ω The voltage and input current I ω Dependency graph between them.

[0028] Figure 5 is the second-order nonlinear Hall effect at different temperatures Data graph.

[0029] Figure 6 This is a schematic diagram of the nonlinear Hall terahertz rectification test device of the present invention.

[0030] Figure 7 It is a diagram of optical rectification voltage signal of the nonlinear Hall terahertz rectification device of the present invention in the terahertz band of 0.02-0.82THz.

[0031] In the figure: 1-substrate; 2-oxide layer; 3-absorption layer. DETAILED DESCRIPTION

[0032] In order to more concisely describe the present embodiment, some parts known to those skilled in the art but not related to the main content of the present invention are omitted in the drawings or descriptions. In addition, for the convenience of description, some parts in the drawings are omitted, enlarged or reduced, but they do not represent the size or entire structure of the actual product.

[0033] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0034] The present invention is further described below in conjunction with the accompanying drawings, which are only used for exemplary description and cannot be understood as limiting the present invention.

[0035] The present invention relates to a nonlinear Hall terahertz rectifier device, such as Figure 1 , Figure 2 As shown, it includes a substrate 1, an oxide layer 2, an absorption layer 3 and an electrode from bottom to top.

[0036] The substrate 1 is made of intrinsic high-resistance silicon, and the high resistivity of the intrinsic high-resistance silicon can effectively reduce the scattering of the substrate to terahertz light; the resistivity of the intrinsic high-resistance silicon of the substrate 1 is 10000-20000Ω·cm, and the thickness is 200-600μm; preferably, the resistivity of the substrate 1 is 20000Ω·cm, and the thickness is 500μm;

[0037] The oxide layer 2 is made of silicon dioxide and has a thickness of 200-500 nm. Preferably, the oxide layer 2 has a thickness of 300 nm.

[0038] The absorption layer 3 is a Weyl semimetal film. The Weyl semimetal is a non-centrosymmetric quantum material. One of the key characteristics of non-centrosymmetric quantum materials is the breaking of inversion symmetry, which leads to the appearance of non-zero Berry curvature in momentum space. Therefore, the integration in the Brillouin zone produces a net Berry curvature dipole, thereby inducing a nonlinear Hall effect.

[0039] Preferably, the Weyl semi-metal film of the present invention is a niobium iridium telluride (NbIrTe4) film. Further, the thickness of the niobium iridium telluride (NbIrTe4) film is 15-100 nm.

[0040] The electrode is a four-terminal metal electrode 4. The four-terminal metal electrode 4 is a composite metal electrode divided into an upper layer and a lower layer. The upper layer metal is gold with a thickness of 45-100nm, and the lower layer metal is chromium with a thickness of 5-25nm. Preferably, the thickness of gold is 75nm, and the thickness of chromium is 15nm.

[0041] The method for preparing the nonlinear Hall terahertz rectifier device as described above comprises the following steps:

[0042] Step 1, preparing niobium iridium telluride (NbIrTe4) single crystal by flux method;

[0043] A specific process for making niobium iridium telluride (NbIrTe4) single crystals is: high-quality niobium iridium telluride (NbIrTe4) single crystals are grown by flux method. Nb powder (purity of 99.99%) and Ir powder (purity of 99.99%) are sealed in a quartz bottle at a molar ratio of 1:1 together with excess Te (purity of 99.999%), and heated to 1000°C under vacuum conditions of 10-6Torr. After being stored at 1000°C for 2 days, the sample is slowly cooled to 700°C and centrifuged at 700°C to remove excess molten Te. Finally, shiny needle-shaped niobium iridium telluride (NbIrTe4) crystals can be harvested under these conditions.

[0044] Step 2: Mechanically exfoliate the niobium iridium telluride (NbIrTe4) single crystal to prepare a niobium iridium telluride (NbIrTe4) thin film with a thickness of 15-100 nm;

[0045] Step 3: transferring the niobium iridium telluride (NbIrTe4) thin film onto the surface of the oxide layer 2 to form an absorption layer 3;

[0046] A specific operation method for making the absorption layer 3 is: use blue film tape (polyvinyl chloride tape) to perform simple mechanical peeling of the niobium iridium telluride (NbIrTe4) single crystal, then use polydimethylsiloxane (PDMS) to adhere the niobium iridium telluride (NbIrTe4) crystal on the blue film tape, and then use dry transfer technology to transfer it to the silicon dioxide surface of the oxide layer 2 to make the absorption layer 3.

[0047] Step 4: using a focused ion beam etching method to etch the niobium iridium telluride (NbIrTe4) film into a cross shape;

[0048] The Weyl semimetal film is etched into a cross-shaped geometric structure using the focused ion beam etching method to ensure the accuracy of the nonlinear Hall effect test. The cross-shaped geometric structure can largely eliminate false contact potential differences such as thermoelectric errors, which affect the measurement of nonlinear Hall voltage.

[0049] Step 5: Apply photoresist on the cross etched on the niobium iridium telluride (NbIrTe4) film, and then use electron beam exposure, electron beam evaporation and stripping methods to make a four-terminal metal electrode to make a nonlinear terahertz Hall device;

[0050] The specific operation is: through electron beam exposure and electron beam evaporation, the lower layer of evaporated metal is chromium, as an adhesion layer, the thickness is preferably 15nm, the upper layer of evaporated metal is gold, the thickness is preferably 75nm, and finally the four-terminal metal electrodes 4 are made at the four tops of the cross etched from the niobium iridium telluride (NbIrTe4) film through traditional stripping technology, thereby making a nonlinear terahertz Hall device.

[0051] Step 6: Place the nonlinear terahertz Hall device made in step 5 on a PCB base, bond wires, and make a nonlinear terahertz Hall rectifier device.

[0052] After the nonlinear terahertz Hall rectifier device is manufactured in step 6, it is necessary to detect the manufactured nonlinear terahertz Hall rectifier device. The detection steps are:

[0053] Step 7, using a low-frequency phase-locked amplification method on the nonlinear terahertz Hall rectifier device prepared in step 6, experimentally observing the generation of a nonlinear Hall effect in a niobium iridium telluride (NbIrTe4) thin film at room temperature;

[0054] The specific operation and detection method is: the nonlinear terahertz Hall rectifier device is packaged into the physical performance tester (PPMS) of Quantum Design Company, such as Figure 3 As shown, using Keithley 6221 ultra-sensitive current source, an alternating current with a frequency of ω = 17.77-1177.77 Hz is applied to the longitudinal axis a of the niobium iridium telluride (NbIrTe4) crystal axis. At the same time, four Stanford lock-in amplifiers SR830 are used to connect to the transverse axis b and longitudinal axis a of the niobium iridium telluride (NbIrTe4) crystal axis respectively to test the voltage signals of the base frequency ω and the frequency multiplication 2ω. Since the non-centrosymmetric quantum material niobium iridium telluride (NbIrTe4) has a strong Berry curvature dipole, it can induce a nonlinear Hall effect, and through Figure 4As shown in part a, NbIrTe4 has good ohmic contact with the electrode, eliminating the Schottky junction rectification effect and the influence of thermoelectricity on the nonlinear Hall effect. Through the quadratic formula fitting, we can see that the longitudinal a-axis current and the transverse b-axis double frequency voltage signal show a good second-order relationship, as shown in Figure 1. Figure 4 In addition, since the b axis of niobium iridium telluride (NbIrTe4) is a mirror axis, the alternating current is applied along the transverse b axis. At the longitudinal a axis, the transverse b axis double frequency voltage is basically zero, as shown in Figure 4 As shown in part c. Therefore, we achieved the first experimental observation of the room temperature nonlinear Hall effect of niobium iridium telluride (NbIrTe4) material.

[0055] like Figure 5 As shown, by lowering the temperature, we found that when an alternating current with a frequency of ω is applied along the longitudinal a-axis, the doubled-frequency voltage obtained along the transverse b-axis will reverse its sign as the temperature decreases. This also shows that the nonlinear Hall effect is directly related to the electronic structure of the Fermi surface.

[0056] Step 8: Based on step 7, a high-frequency terahertz wave rectification experiment is performed, a linear terahertz wave is applied along the longitudinal direction of the device, and a direct current signal is collected in the transverse direction of the device.

[0057] like Figure 6 , Figure 7 As shown, after the experiment verified the existence of the nonlinear Hall effect in the nonlinear Hall terahertz rectifier of the present invention, we used this mechanism to test the terahertz photoelectric response: by combining a microwave source (0.02-0.04THz) and a VDI frequency multiplier link, it can emit 0.10-0.12THz, 0.24-0.30THz, 0.43-0.46THz, 0.49-0.54THz, and 0.74-0.82THz. The terahertz radiation light is irradiated onto the entire surface of the rectifier, and the rectifier converts the AC electromagnetic wave signal into a DC signal, introduces a current amplifier (SR570) to amplify the signal, and reads the rectified voltage signal through a phase-locked amplifier (SR830), wherein the modulation frequency signal built into the microwave source (E8257D) is input into the phase-locked amplifier as a reference signal.

[0058] Compared with the prior art, the nonlinear Hall terahertz rectifier device of the present invention has the following advantages: from the perspective of material structure, the Weyl semimetal niobium iridium telluride (NbIrTe4) itself has strong anisotropy and inversion symmetry breaking, and exhibits strong Weyl nodes and unique topological characteristics. Combined with the four-terminal metal electrode 4, the longitudinal oscillating terahertz light field is rectified into a transverse junctionless photoelectric signal, thereby improving the signal-to-noise ratio and achieving high-sensitivity terahertz detection.

[0059] From a mechanistic point of view, in the absence of any external field, the contribution of the intrinsic Berry curvature dipole induces a nonlinear Hall effect in non-centrosymmetric quantum materials, ultimately achieving wide-spectrum photoelectric rectification results under the terahertz light field.

[0060] In summary, the nonlinear Hall terahertz rectifier device of niobium iridium telluride (NbIrTe4) and its preparation method provided by the present invention not only reveal the potential mechanism of driving efficient low-energy photon collection through the nonlinear Hall effect, but also pave the way for the development of dissipative optoelectronic devices based on non-magnetic quantum materials in the infrared / terahertz band, and are expected to break through the technical bottleneck of traditional room-temperature terahertz detection.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. That is, any equivalent changes and modifications made according to the content of the patent application scope of the present invention should be within the technical scope of the present invention.

Claims

1. A nonlinear Hall terahertz rectifier device, comprising, from bottom to top, a substrate (1), an oxide layer (2), an absorption layer (3) and an electrode; characterized in that: The substrate (1) is made of intrinsic high-resistance silicon, the oxide layer (2) is made of silicon dioxide, the absorption layer (3) is a Weyl semi-metal film, and the electrode is a four-terminal metal electrode (4).

2. The nonlinear Hall terahertz rectifier device according to claim 1, characterized in that: Weyl semimetal thin film is niobium iridium telluride thin film.

3. The nonlinear Hall terahertz rectifier device according to claim 2, characterized in that: The thickness of the niobium, iridium and tellurium film is 15-100nm.

4. The nonlinear Hall terahertz rectifier device according to claim 1, characterized in that: The resistivity of the substrate (1) is 10000-20000Ω·cm, and the thickness is 200-600μm; the thickness of the oxide layer (2) is 200-500nm.

5. The nonlinear Hall terahertz rectifier device according to claim 4, characterized in that: The resistivity of the substrate (1) is 20000Ω·cm and the thickness is 500μm; the thickness of the oxide layer (2) is 300nm.

6. The nonlinear Hall terahertz rectifier device according to claim 1, characterized in that: The four-terminal metal electrode (4) is a composite metal electrode divided into an upper layer and a lower layer. The upper layer metal is gold with a thickness of 45-100 nm, and the lower layer metal is chromium with a thickness of 5-25 nm.

7. The nonlinear Hall terahertz rectifier device according to claim 6, characterized in that: The thickness of gold is 75nm and the thickness of chromium is 15nm.

8. A method for preparing a nonlinear Hall terahertz rectifier device according to any one of claims 2 to 7, characterized in that: The method comprises the following steps: Step 1, preparing niobium iridium telluride single crystal by flux method; Step 2: Mechanically exfoliate the niobium iridium telluride single crystal to prepare a niobium iridium telluride (NbIrTe4) thin film with a thickness of 15-100 nm; Step 3: transferring the niobium, iridium and tellurium thin film onto the surface of the oxide layer (2) to form an absorption layer (3); Step 4: using a focused ion beam etching method, etching the absorption layer (3) made of the niobium iridium telluride thin film into a cross shape; Step 5: applying photoresist on the cross shape etched on the absorption layer (3), and then sequentially performing electron beam exposure, electron beam evaporation and stripping steps to form a four-terminal metal electrode (4), thereby completing the production of a nonlinear terahertz Hall device; Step 6: Place the nonlinear terahertz Hall device made in step 5 on a PCB base, bond wires, and make a nonlinear terahertz Hall rectifier device.

9. The method for preparing the nonlinear Hall terahertz rectifier according to claim 8, characterized in that: After step six, a detection step is also included, and the detection step is: Step 7: Using a low-frequency phase-locked amplification method on the nonlinear terahertz Hall rectifier device prepared in step 6, experimentally observing the generation of a nonlinear Hall effect in the niobium, iridium and telluride thin film at room temperature; Step 8: Based on step 7, a high-frequency terahertz wave rectification experiment is performed, a linear terahertz wave is applied along the longitudinal direction of the device, and a direct current signal is collected in the transverse direction of the device.

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