Room-temperature topological insulator heterojunction photodetector with a special dipole antenna

Abstract

The present invention discloses a room-temperature topological insulator heterojunction photodetector with a special dipole antenna. The device preparation steps are as follows: transfer the germanium-bismuth-tellurium grown by chemical vapor deposition onto a high-resistance silicon substrate with a silicon dioxide oxide layer, then use dry transfer to form a heterojunction between bismuth telluride material and germanium tellurium bismuth, and then use ultraviolet lithography technology to fabricate source and drain electrodes, and use processes such as ultraviolet lithography, electron beam evaporation, and lift-off to prepare a topological insulator heterojunction photodetector with a special antenna structure. By using the unique antenna structure, the terahertz field is concentrated on the incident device, realizing the enhancement of the collective plasmon oscillation efficiency and absorption under the control of the sub-wavelength scale photon structure, and greatly improving the sensitivity of the photodetector. The photodetector described above exhibits ultra-high responsivity and a relatively wide response spectrum in the terahertz band. The advantages of the present invention are high detectivity, fast response, wide-spectrum response, low power consumption, and ease of integration.

Description

Technical Field

[0001] This patent relates to a room-temperature topological insulator heterojunction photodetector integrated with a special dipole antenna structure and a preparation method thereof. Specifically, a photodetector based on topological insulator germanium bismuth telluride is designed in a planar form of a novel special dipole antenna, and electrical and optical tests are carried out thereon. The dipole antenna structure is also used as an electronic readout electrode. The antenna electrode is asymmetric, which converts the propagating electromagnetic wave into localized surface plasmon polaritons, enabling the local light field at one end of the electrode to be greatly enhanced, thereby realizing the strong localization of the plasmon-induced electric field at the metal-topological insulator interface, improving the detection sensitivity of the device, and broadening the response spectrum of the device. Background Art

[0002] Terahertz radiation (0.1 - 10 THz) can connect electronic devices and optical devices, covering a wide-band electromagnetic spectrum from microwaves to infrared light. Its hybrid characteristics enable a wide range of applications, including wireless communication, sensing, and imaging. With the emergence of emerging two-dimensional materials such as graphene, transition metal dichalcogenides (TMDCs), topological materials, and three-dimensional Dirac systems, the exploration of the unique electrical and optical properties of these materials has promoted the development of terahertz optoelectronic devices. Among them, topological materials are characterized by massless Dirac fermions and exhibit unique broadband response characteristics. However, terahertz detectors based on graphene and black phosphorus materials have disadvantages such as slow response speed, instability, and the need for cryogenic cooling.

[0003] Topological materials have important value in high-performance, broadband, and room-temperature optoelectronic devices due to their special topological surface states and dissipationless electron transport characteristics. Based on the topological properties of the electronic band structure in momentum space, topological materials are classified into topological insulators (TI), Dirac semimetals (DS), Weyl semimetals (WS), and nodal line semimetals (NLS) by introducing topological invariants. The carriers of topological insulators have extremely low energy losses during the surface state transport process, resulting in ultra-high carrier mobility, making them suitable for high-speed, low-energy electronic and optoelectronic devices. Currently, based on Bi 2 Se 3 、Bi 2 Te 3 and Sb 2 Te 3 Photodetectors in topological insulators have been studied and the responsivity is higher than that of graphene devices. The response mechanisms include overdamped plasma waves and asymmetric scattering of topological surface states. With the emergence of topological materials, based on Bi 2 Te3 The detector of has been studied as an excellent topological material for room-temperature applications, which is facilitated by its semimetal properties. However, Bi 2 Te 3 has a Fermi surface without isolated Dirac points, but independent Dirac points can be achieved by inserting some additional Ge-Te layers into the material. GeBi 4 Te 7 has the same chemical potential as Bi 2 Te 3 and has a larger Fermi momentum, resulting in a larger surface carrier density. Due to the high density of the complex electronic structure near the Fermi energy, doped topological insulators have a higher Seebeck coefficient, which is beneficial for terahertz detection. However, the photosensing ability of GeBi 4 Te 7 has never been studied, so exploring its applications in terahertz detection and imaging is a meaningful direction. Therefore, germanium bismuth telluride, as a topological insulator, has important application prospects in the field of terahertz technology, providing a good research platform for the next generation of optoelectronic devices. In addition, the surface of two-dimensional materials has no dangling bonds, so there will be no problem of lattice mismatch when forming van der Waals heterojunctions, which can also shorten the conduction path and increase the photoconductive gain. Therefore, constructing van der Waals heterojunctions can effectively reduce the dark current and improve the responsivity of the detector.

[0004] Existing photodetectors usually detect high-energy photons above the bandgap energy through the photoconductive or photovoltaic effect. However, theoretically, for any specific wavelength, detection can be achieved through thermal effects such as the pyroelectric effect, photothermal electricity (PTE), and pyroelectric effect, without being limited by the bandgap. Among these photodetectors, detectors based on the photothermal electricity effect are considered viable candidates for terahertz detection because they have the advantages of simple geometry, zero-bias operation, and low power consumption. So far, there are mainly three methods to enhance the performance of photothermal electricity detectors. Polariton excitons such as surface plasmons in metals can be utilized, and cavities or waveguides can be incorporated into the photodetector to enhance the light-matter interaction. The most effective and simple method is based on the principle of an antenna, introducing a functional structure, either by converting free-propagating light radiation into local energy or by matching the surface impedance of the material with light to enhance light absorption. Therefore, designing an efficient planar antenna is a feasible and effective method to enhance the performance of photothermal electricity detectors. Summary of the Invention

[0005] This patent proposes a preparation method of an asymmetric dipole antenna integrated terahertz detector at room temperature. Using a unique antenna structure, the terahertz field is concentrated on the incident device, and due to the temperature gradient generated at the source and drain ends, the photo-generated carriers are driven to move to form a directional current, achieving self-driven high-sensitivity and wide-band light detection at room temperature.

[0006] The structure of the detector is as follows: from bottom to top, a silicon dioxide layer 2 is on a high-resistance silicon substrate (1), a two-dimensional material heterojunction formed by bismuth germanium telluride 4 and bismuth telluride 5 is on the silicon dioxide layer, source electrode 3 and drain electrode 6 are at both ends of the heterojunction, and its structure consists of an asymmetric dipole metal antenna, with the left antenna electrode 3 and the right antenna electrode in a fan-shaped structure. The source-drain spacing is 2 - 4 μm, and the left and right dipole antennas are asymmetric, which can enhance the local light field.

[0007] The substrate 1 is intrinsic high-resistance silicon with a resistivity of 20000 - 30000 Ω·cm;

[0008] The thickness of the silicon dioxide layer 2 of the oxide layer is 200 - 300 nm;

[0009] The thickness of the bismuth germanium telluride nanosheet 4 is 50 - 70 nm;

[0010] The thickness of the bismuth telluride 5 nanosheet is 70 - 100 nm;

[0011] The antenna structure: the source electrode 3 and the drain electrode 6 form an asymmetric dipole antenna structure, and the pattern of the antenna is obtained by standard ultraviolet lithography technology, and then a Cr / Au (thickness range 90 - 110 nm) thin film is evaporated using thermal evaporation coating technology.

[0012] The present invention relates to a terahertz detector based on an asymmetric dipole antenna integrated topological insulator heterojunction at room temperature and a preparation method thereof. The preparation of the device includes the following steps: First, use a low-viscosity tape to transfer the synthesized novel topological insulator single crystal bismuth germanium telluride (GeBi 4 Te 7 ) bulk material onto a high-resistance silicon substrate by mechanical exfoliation method, and then use dry transfer to contact the mechanically exfoliated bismuth telluride (Bi 2 Te 3 ) material with bismuth germanium telluride to form a heterojunction; then use ultraviolet lithography technology, electron beam evaporation coating process and traditional lift-off process to prepare an asymmetric dipole antenna structure, at this time the source and drain electrodes are respectively in contact with one end of bismuth germanium telluride and bismuth telluride; then attach the device to the base, complete the encapsulation through ultrasonic wire bonding process, and finally form a terahertz detector based on an asymmetric dipole antenna integrated topological insulator heterojunction.

[0013] The advantages of this invention patent are as follows:

[0014] 1) The channel material selected is a topological insulator. This material has conductive surface states (semi-metallic property) and insulating bulk energy bands, endowing this type of material with the ability to be used in terahertz detectors for broadband and high-speed optical response.

[0015] 2) Germanium bismuth telluride and bismuth telluride materials have the advantages of environmental stability, scalability, and inexpensive raw materials. Heterojunction devices with high efficiency and low material surface contamination can be prepared through the fixed-point transfer technology.

[0016] 3) By adopting a special dipole antenna structure that is easy to integrate, the electromagnetic waves in the sub-wavelength channel are super-focused, and the optical field is highly localized, which can effectively enhance the interaction between terahertz waves and Dirac electron gas.

[0017] 4) By leveraging the advantage of the vertical stacking of two-dimensional materials without lattice mismatch to construct a van der Waals heterojunction, due to the difference in the Seebeck coefficients of the two, non-equilibrium carriers can move directionally, and the self-driven photothermal-electric effect can be utilized to operate efficiently and stably at room temperature.

[0018] 5) The topological insulator germanium bismuth telluride and bismuth telluride heterojunction device has the technical advantages of low dark current, low noise equivalent power, and fast response time, and has successfully realized the terahertz transmission imaging application of metal materials at room temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 FIG. is a schematic side view of the structural unit of the terahertz detection device based on the topological insulator heterojunction integrated with a room-temperature asymmetric dipole antenna of the present invention;

[0020] Figure 2 FIG. is a schematic top view of the structure of the terahertz detection device based on the topological insulator heterojunction integrated with a room-temperature asymmetric dipole antenna of the present invention;

[0021] Figure 3 FIG. is the optical response spectrum of the terahertz detector based on the topological insulator heterojunction integrated with a room-temperature asymmetric dipole antenna of the present invention under zero bias voltage;

[0022] Figure 4 FIG. is a schematic diagram of the response time of the terahertz detector based on the topological insulator heterojunction integrated with a room-temperature asymmetric dipole antenna of the present invention under zero bias voltage;

[0023] Figure 5 FIG. is a schematic diagram of the change of the responsivity of the terahertz detector based on the topological insulator heterojunction integrated with a room-temperature asymmetric dipole antenna of the present invention with the bias voltage at different frequencies;

[0024] Figure 6 FIG. is a schematic diagram of the change of the noise of the terahertz detector based on the topological insulator heterojunction integrated with a room-temperature asymmetric dipole antenna of the present invention with the bias voltage at room temperature. DETAILED DESCRIPTION OF THE INVENTION

[0025] The following provides a detailed description of the specific embodiments of the present invention in conjunction with the accompanying drawings:

[0026] The present invention relates to a preparation method, mechanism research, and performance improvement of a terahertz detector based on a topological insulator heterojunction integrated with a room-temperature asymmetric dipole antenna. Specifically, it refers to using topological insulator germanium bismuth telluride (GeBi 4 Te 7 ) and bismuth telluride (Bi 2 Te 3 ) to construct a van der Waals heterojunction in the horizontal direction. Through the integrated simulation design of a novel asymmetric dipole antenna, terahertz waves are efficiently focused to form an electric potential gradient at both ends of different materials, driving the flow of non-equilibrium carriers, greatly reducing the dark current and noise equivalent power of the device, and thus realizing a self-driven working mode and terahertz transmission imaging application for metal objects at room temperature.

[0027] The specific steps are as follows:

[0028] The preparation method of a terahertz detector based on a room-temperature asymmetric dipole antenna integrated with a topological insulator heterojunction of the present invention is as follows:

[0029] 1. Substrate selection

[0030] Select intrinsic high-resistivity silicon 1 and thermally grown silicon dioxide 2 covering it;

[0031] 2. Preparation and characterization of germanium bismuth telluride material

[0032] High-quality germanium bismuth telluride (GeBi 4 Te 7 ) crystals were synthesized by the chemical vapor transport (CVT) method. The synthesis process is as follows. Germanium powder (99.999%, Aladdin Chemicals), bismuth powder (99.99%, damas-beta), and tellurium powder (99.999%, Aladdin Chemicals) were uniformly mixed in a stoichiometric ratio of 1:4:7 and then sealed in the hot zone of a quartz tube under a vacuum of about 2.5×10 -2 Pa. An appropriate amount of I 2 (99.99%, Aladdin Chemicals) was selected as the transport agent. Then, the temperatures of the hot zone and the cold zone were heated to 750°C and 650°C at a rate of 1°C / min and maintained for 7 days. After natural cooling, GeBi 4 Te 7 crystals were harvested in the cold zone, and then the morphology and structure of germanium bismuth telluride were microscopically characterized by XRD, TEM, EDS, Raman, etc.;

[0033] 3. Preparation of the heterojunction

[0034] The mechanical exfoliation method was used to exfoliate Bi 2 Te 3 and GeBi 4 Te7 A material with nanoscale thickness is exfoliated from a bulk crystal, and then GeBi 4 Te 7 is transferred onto a substrate, and the layered Bi 2 Te 3 is transferred from the blue tape onto polydimethylsiloxane (PDMS). Then, under an optical microscope of a precision transfer platform (E1-T), the layered Bi 2 Te 3 is transferred onto GeBi 4 Te 7 by dry transfer, and one end of the two materials is brought into contact to complete the preparation of the heterojunction.

[0035] 4. Device Fabrication and Exfoliation

[0036] An electrode structure is formed on the substrate by ultraviolet lithography (MA6), then 90 - 110 nm Cr / Au contacts are deposited by electron beam evaporation, and finally, GeBi 4 Te 7 -Bi 2 Te 3 topological insulator heterostructure room-temperature terahertz detector ( Figure 1 and Figure 2 ).

[0037] 5. Device Encapsulation

[0038] The device is fixed on a PCB base by soldering with an electric soldering iron, and the base and the device are welded together by an electric welder to fabricate an asymmetric dipole antenna integrated topological insulator heterojunction terahertz detector.

[0039] 6. Device Performance Testing

[0040] The electrical characteristics of the device are measured using a semiconductor parameter analyzer. A microwave generator is used to generate low-frequency microwaves, and electromagnetic waves in the range of 0.02 - 0.54 THz are generated through a multiplication link. The optical response is recorded by a lock-in amplifier (LIA) and an oscilloscope after a low-noise voltage preamplifier. The specific operation is to use the pulse signal modulation frequency of the microwave source as the reference signal source for the lock-in amplifier and the oscilloscope, and at the same time, the photoelectric signal of the detector amplified by the preamplifier is connected to the input port of the lock-in amplifier, and the output signal is the signal amplified again by the lock-in. Through this system, the signal-to-noise ratio can be improved, and the automated test functions such as the response signal of the terahertz detector and the response time of the detector can be realized. Figure 3 The terahertz response spectra of the device under zero bias are shown, and the response spectra of the devices with source-drain spacings of 2 μm, 3 μm, and 4 μm are tested respectively. We use a high-speed oscilloscope to collect the response time, Figure 4Response time graph of a terahertz detector based on a topological insulator heterojunction integrated with an asymmetric dipole antenna at zero bias voltage. It is usually calculated as the amount of time required for the optical response of a single pulse to increase from 10% to 90% or decrease from 90% to 10%. The turn-on time of the device is approximately 10 μs, the turn-off time is approximately 6 μs, and the waveform is complete with a low signal-to-noise ratio. The power density of the terahertz radiation is calibrated by a Golay cell. The detector responsivity (R V ) is calculated through the relation R V = ΔV / P in = ΔV / S a ·P, where P in is the incident power, S a is the effective area, and P in is the power density. Figure 5 shows the curves of the voltage responsivity varying with the bias voltage at 0.112 THz, 0.27 THz, and 0.5 THz. The maximum responsivities of the device at 0.112 THz, 0.27 THz, and 0.5 THz are 592 V / W, 203 V / W, and 40 V / W respectively. The equivalent noise power (NEP) is a figure of merit used to evaluate the performance of the device and can be estimated from NEP = V n / R V , corresponding to the minimum detectable power at a 1 Hz bandwidth. Figure 6 shows the NEP values of the device corresponding to the above frequencies respectively.

[0041] The terahertz detector based on a topological insulator heterojunction integrated with a special dipole antenna in the present invention can significantly improve the overall optical response of the device, such as reducing the dark current noise, broadening the detector response frequency band, having a response time in the microsecond level, a relatively high voltage responsivity, an extremely low power consumption, self-powered, etc. The results show that the terahertz detector based on a topological insulator heterojunction integrated with a special dipole antenna at room temperature in the present invention may be an ideal way to realize the application of quantum material technology in the terahertz range with great promise.

Claims

1. A room-temperature topological insulator heterojunction photodetector with a special dipole antenna, comprising an Si substrate (1), SiO 2 oxide layer (2), germanium bismuth telluride (4), and bismuth telluride (5). It is characterized in that: The described detector structure: An SiO 2 oxide layer (2) is provided on an Si substrate (1), and 2 a germanium bismuth telluride (4) and a bismuth telluride (5) are prepared on the SiO oxide layer (2). The germanium bismuth telluride (4) and the bismuth telluride (5) form a heterojunction. A source electrode (3) is provided at one end of the germanium bismuth telluride (4), and a drain electrode (6) is provided at one end of the bismuth telluride (5). Its structure consists of an asymmetric dipole antenna, and the distance between the source and the drain is 2 - 4 μm; The substrate (1) is intrinsic high-resistance silicon with a resistivity of 20,000 - 30,000 Ω·cm and a thickness of 500 - 600 μm; on which silicon dioxide (2) is covered with a thickness of 200 - 300 nm; The germanium bismuth telluride (4) is a germanium bismuth telluride nanosheet with a thickness of 50 - 70 nm; The bismuth telluride (5) is a bismuth telluride nanosheet with a thickness of 70 - 100 nm; The source electrode (3) and the drain electrode (6) of the antenna structure are metal composite electrodes. The lower layer metal of the metal composite electrode is chromium (Cr), the upper layer metal of the metal composite electrode is gold (Au), and the thickness range of the metal composite electrode is 90 - 110 nm.

2. A method for preparing the photodetector as described in claim 1, It is characterized in that The method is as follows: The channel material of the device, two-dimensional germanium bismuth telluride crystal, is grown by chemical vapor deposition method. The germanium bismuth telluride nanosheet with nanoscale thickness is obtained by micro-mechanical exfoliation technology and transferred to the substrate surface; then the single crystal bismuth telluride is transferred to polydimethylsiloxane by mechanical exfoliation and transferred to contact with one end of the germanium bismuth telluride nanosheet with the help of a two-dimensional material transfer platform; Then the asymmetric dipole antenna structure is prepared by ultraviolet lithography technology, electron beam evaporation coating process and traditional lift-off process. The source electrode is in contact with one end of the germanium bismuth telluride, and the drain electrode is in contact with one end of the bismuth telluride (5); finally, the device is packaged by ultrasonic wire bonding process to form a terahertz detector of an asymmetric dipole antenna integrated topological insulator heterojunction.

Images