Terahertz radiation detector

Abstract

The invention relates to the field of optical engineering, and more particularly to detectors of terahertz (THz) radiation (having a frequency of 0.1-10 THz or a wavelength of 30-3000 μm), and can be used for the broadband detection of pulsed or continuous THz radiation or for measuring the power thereof. The technical result achieved by the invention consists in permitting high-sensitivity detection of continuous and pulsed THz radiation having a power of up to 500 mW at a temperature of from -10°C to +50°C in a frequency range of 0.1-10 THz with a sensitivity of not less than 30 mV / W, a noise equivalent power of at least 0.15 nW⋅Hz-1 / 2, a response time of not more than 20 μs and a modulation frequency of 1-40 Hz. This technical result is achieved by the use in the detector structure of a thermoelectric material that is highly sensitive to radiation in the THz frequency range, and also by the absence of resonant elements, such as an antenna and a metasurface, the use of which would cause the spectrum of detectable radiation to be narrowed to a specific frequency range. As a sensitive thermoelectric element, it is proposed to use thermoelectric branches made of a thin film of a solid solution of bismuth-antimony Bi1-xSbx.

Description

[0001] TERAHERTZ RADIATION DETECTOR

[0002] Description of the invention

[0003] Field of technology to which the invention relates

[0004] The invention relates to the field of optical engineering, namely to detectors of terahertz (THz) radiation (with a frequency of 0.1-100 THz or a wavelength of 30-3000 μm), and can be used for broadband detection of pulsed or continuous THz radiation or measuring its power.

[0005] Prior art

[0006] The development of many areas of THz photonics, such as wireless communications, visualization systems, contactless diagnostics and quality control in medicine, pharmaceuticals, food industry and security systems, requires the implementation of THz radiation detection devices that would operate at room temperature, in a broadband mode, and would provide detection of both continuous and pulsed THz radiation.

[0007] One of the ways to effectively solve this problem is to use detectors based on thermoelectric materials with high sensitivity to THz radiation in a wide frequency range. Such detectors have a simple structure and can operate at room temperature [Bai J. et al. A terahertz photo-thermoelectric detector based on metamaterial absorber / / Optics Communications. - 2021 . - V. 497. - P. 127184].

[0008] Among the patent literature, detectors are known based on field-effect transistors, the channel of which is a network of carbon nanotubes, and the broadband excitation of damped plasma waves is considered as the main detection mechanism, while the thermoelectric and diode effects contribute to the observed response [RU194869, RU186169]. The declared operating frequency range of such detectors is 0.1-5-2 THz, the operating temperature range is 4.2-5-300 K, the sensitivity is not worse than 30 V / W at a frequency of 0.129 THz, the equivalent noise power is not worse than 1 nW THz. 172 . Thus, such detectors can operate in a broadband mode, but in the low-frequency region of the TG range.

[0009] A thermoelectric detector of THz radiation frequency range based on an antenna and a field-effect transistor with a channel made of thin films of black phosphorus doped with selenium is also known [Viti L. et al. Thermoelectric terahertz photodetectors based on selenium-doped black phosphorus flakes / / Nanoscale. - 2019. - Vol. 11. - No. 4. - P. 1995-2002]. The possibility of detection using it has been demonstrated at a frequency of 3.4 THz at room temperature, the sensitivity is 3 V / W, the equivalent noise power is 7 nW -1 / 2 The optimal thickness of the sensitive element is 30-5-40 nm.

[0010] A type of thermoelectric THz radiation detectors is known based on an asymmetric antenna and a field-effect transistor with a channel made of a nanowire with sequentially located InAs / InAsO.sPo,? quantum dots with different band gaps [Asgari M. et al. Quantum-Dot Single-Electron Transistors as Thermoelectric Quantum Detectors at Terahertz Frequencies / / Nano Letters. - 2021 . - V. 21 . - No. 20. - Pp. 8587-8594]. In this work, the antenna geometry and detector parameters were adjusted to detect radiation with a frequency of 0.6 THz, which is possible only at ultra-low temperatures and was studied at a temperature of 4.2 K. Such a detector has a sensitivity of 55 μA / W, equivalent to a noise power of 8 pW Hz' 1 / 2 , with a response time of 1-10 ns, but is difficult to manufacture and cannot operate at room temperature, and only works in a narrow frequency range.

[0011] In the paper [Szakmany G. P. et al. THz wave detection by antenna-coupled nanoscale thermoelectric converters / / IEEE Transactions on Terahertz Science and Technology. - 2017. - V. 7. - No. 5. - P. 582-585] a thermoelectric THz detector is presented based on a gold dipole antenna with a narrow central part, the heating of which by THz radiation leads to the appearance of a voltage on nanothermocouples located close to the center of the antenna, while an increase in the number of series-connected nanothermocouples leads to an increase in the sensitivity of such a detector. The detector presented in this paper is designed for narrowband detection at a frequency of 0.6 THz at room temperature and is characterized by high polarization sensitivity.

[0012] The work [Shabanov A. et al. Optimal asymmetry of transistor-based terahertz detectors / / Applied Physics Letters. - 2021. - V. 119. - No. 16. - P. 163505] is devoted to the optimization of the sensitivity of THz detectors based on graphene asymmetric field-effect transistors using the thermoelectric effect, but only at a frequency of 0.13 THz, corresponding to the geometry of the coupled antenna. The possibility of detection in this work is presented at temperatures of 77 and 300 K, and the sensitivity in both cases reaches 9 V / W.

[0013] The authors of the patent [US 10969335] claim the possibility of detecting THz radiation using the thermoelectric effect as the main detection mechanism: in the detector structure, electrodes with different thermal conductivity are connected to a grid of carbon nanotubes on two opposite sides. Although the theoretical possibility of absorption of radiation from ultra-low to ultraviolet frequencies by carbon nanotubes is mentioned, the said patent shows the possibility of detection at fixed frequencies: 0, 14 THz, 1.4 THz, 14 THz, 29 THz, 30 THz, the equivalent noise power of no worse than 700 pW THz is claimed. -1 / 2 .

[0014] In the work [He X. et al. Carbon nanotube terahertz detector / / Nano letters. - 2014. - V. 14. - №. 7. - P. 3953-3958] a similar thermoelectric TH detector is presented based on the contact of doped highly oriented long carbon nanotubes of the n- and p-type, located parallel to each other and connected to gold electrodes. The possibility of detection is demonstrated at room temperature for fixed frequencies of 1.39 THz, 2.52 THz and 3.11 THz, the sensitivity is 2.5 V / W, the equivalent noise power is not worse than 20 nW. -1 / 2 , however, it should be noted that the manufacturing of such a detector is more complex. The Seebeck coefficient is 71 75 μV / K.

[0015] In the work [Ahmad H., Suzuki D., Kawano Y. Strain-induced photo-thermoelectric terahertz detection / / AIR Advances. - 2018. - Vol. 8. - No. 11. - P. 115002] a thermoelectric detector based on a deformed strip of carbon nanotubes connected to gold electrodes is presented, while an increase in the Seebeck coefficient to 161 μV / K compared to a similar flat structure (36 μV / K) is associated with the magnitude of the strip deformation, leading to the transition of the nanotube state from metallic to semiconductor. Measurements in this work were carried out only at fixed frequencies of 1.4 THz and 29 THz at room temperature. The thickness of the carbon nanotube layer is 40-150 μm.

[0016] In addition, a type of graphene-based detectors is known [US10084102] [Cai X. et al. Sensitive room-temperature terahertz detection via the photothermoelectric effect in graphene / / Nature nanotechnology. - 2014. - V. 9. - No. 10. - P. 814-819], where the photothermoelectric effect, enhanced by excitation of plasma waves in graphene microstrips by THz radiation, is considered as the main detection mechanism. However, such detection is carried out only in a narrow frequency range for quasi-monochromatic THz radiation, since the plasma frequency in graphene microstrips is matched to the frequency of the incident THz radiation by varying the width of such strips and by controlling the density of charge carriers by exposure to a constant electric field. In addition, a clear spatial orientation of the detector relative to the polarization of the THz waves incident on it is necessary to ensure the possibility of excitation of plasmon resonance.This detector operates at room temperature and has an equivalent noise power of 1.1 nW / c. -1 / 2 and a sensitivity of over 10 V / W (relative to the absorbed power) at a frequency of detected radiation of 2.52 THz, has a response time of 110 ps. The indicated work mentions the possibility of broadband (integral) detection in the frequency range of 0+2 THz, but does not present the dependence of sensitivity on the frequency of THz radiation.

[0017] A similar type of THz thermoelectric detectors is known [CN107482109A] based on a single asymmetric graphene dipole antenna with a resonant frequency band of 1+3 THz, connected to ohmic contacts made of materials with different thermal conductivity (Au, Ti). A similar detector is presented in the work [Tielrooij K. J. et al. Highly sensitive, ultrafast photo-thermoelectric graphene thz detector / / 201843rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz). - IEEE, 2018. - P. 1- 3], where a connection of two doped graphene sheets encapsulated with hexagonal boron nitride (hBN) is used, and the detected frequency range corresponds to 2+4 THz, the equivalent noise power is not worse than 200 pW c' 1 / 2, response time less than 40 ns (Seebeck coefficient for graphene up to 100 μV / K). Other similar graphene-based detectors are presented in the work [Viti L. et al. Thermoelectric graphene photodetectors with sub-nanosecond response times at terahertz frequencies / / Nanophotonics. - 2021. - V. 10. - No. 1. - P. 89-98] for a frequency of 3.4 THz (equivalent noise power up to 120 pW Hz -1 / 2 , sensitivity up to 10+20 V / W, operation at room temperature), in the work [Tong J. et al. Antenna enhanced graphene THz emitter and detector / / Nano Letters. - 2015. - V. 15. - No. 8. - P. 5295-5301] for a frequency of 1.9 THz (equivalent noise power up to 1.7 nW-Hz' 172 , sensitivity up to 4.9 V / W, operation at room temperature), in the work [Liu C. et al. Towards sensitive terahertz detection via thermoelectric manipulation using graphene transistors / / NPG Asia Materials. - 2018. - V. 10. - No. 4. - P. 318-327] for a frequency of 0.12 THz (equivalent noise power up to 100 pW THz -1 / 2, sensitivity up to 280 V / W, operation at room temperature), in the work [Bauer M. et al. The potential for sensitivity enhancement by the thermoelectric effect in carbon-nanotube and graphene Tera-FETs / / Journal of Physics: Conference Series. - IOP Publishing, 2015. - Vol. 647. - No. 1. - P. 012004] for a frequency of 0.6 THz (equivalent noise power up to 515 pW Hz' 1 / 2 , operation at room temperature). Such detectors operate only in a relatively narrow frequency range, determined by the geometry of the antenna and the properties of the materials used in it.

[0018] Another type of THz thermoelectric detectors is known [CN111854941 A], where graphene acts as an absorber of THz waves, while lead zirconate titanate, lithium tantalate, lithium niobate, gallium nitride and cesium nitrate act as thermoelectric materials. The manufacturing method described in the said patent (a multilayer structure with ultra-thin layers of graphene on a substrate, thin layers of microparticles, thermoelectric material and electrodes) is technologically complex and therefore requires high costs.

[0019] A type of THz thermoelectric detectors based on MAPbh perovskite single crystals (gold and silver electrodes are connected to two opposite sides of the single crystal) with an anti-reflection coating based on two-dimensional perovskite, which also operate at room temperature, is known [Li J. et al. Enhanced room-temperature terahertz detection and imaging derived from anti-reflection 2D perovskite layer on MAPbh single crystals / / Nanoscale. - 2022. - V. 14. - No. 16. - P. 6109-6117], characterized by an equivalent noise power of less than 2.16 nW THz -1 / 2 , with a sensitivity of 88.8 μA / W. However, the possibility of detection using the specified material was demonstrated only for a frequency of 0.1 THz in the specified work.

[0020] In the work [Bai J. et al. A terahertz photo-thermoelectric detector based on metamaterial absorber / / Optics Communications. - 2021. - V. 497. - P. 127184] a type of thermoelectric THz detectors based on a gold and bismuth thermocouple is presented, at the junction of which a metasurface is located, which is a selective absorber of THz radiation at a resonant frequency of 1 THz. This detector is characterized by an equivalent noise power of 6.6 μW THz' 172 , with a sensitivity of 35 mV / W. Despite the ability to operate at room temperature, this configuration is not intended for broadband detection of THz radiation.

[0021] In connection with the above, at present, a pressing task is to develop a detector of pulsed and continuous THz radiation based on a thermoelectric material, operating at room temperature, which provides broadband detection in the entire THz frequency range (0.1 +10 THz), while having a simple design.

[0022] The essence of the invention

[0023] The objective of the present invention is to develop a compact device that provides detection of both continuous and pulsed THz radiation in the frequency range from 0.1 THz to 10 THz at room temperature.

[0024] The technical result achieved by the claimed invention consists in providing the possibility of highly sensitive detection of continuous and pulsed THz radiation with a power of up to 500 mW at a temperature from -10 °C to +50 °C in the frequency range of 0.1+10 THz with a sensitivity of at least 30 mV / W, equivalent to a noise power of no worse than 0.15 nW THz. -172 , response time no more than 20 μs, modulation frequency 1+40 Hz.

[0025] The main elements of the device are a lens, thermoelectric branches based on thin-film thermoelectric material, and an amplifier board connected to electrodes at both ends of the coil.

[0026] The device operates as follows: pulsed or continuous THz radiation hits a sensitive element made in the form of thermoelectric branches based on thin films of a bismuth-antimony solid solution and connected at both ends to electrodes (contacts), and causes its uneven heating, resulting in a thermo-EMF (photothermoelectric effect), and the value of the potential difference is amplified by the amplification board and transmitted to the external interface for reading by an external voltage measuring device.

[0027] The above technical result is achieved by the fact that the detector structure uses a thermoelectric material with high sensitivity to radiation in the THz frequency range, as well as due to the absence of resonant elements, such as antennas and metasurfaces, the use of which would lead to a narrowing of the spectrum of the detected radiation to a certain frequency range. It is proposed to use thermoelectric branches made of a thin film of a solid solution of bismuth-antimony BiI as a sensitive thermoelectric element. x Sb x .

[0028] List of figures, drawings The invention is explained by a schematic drawing presented in Fig. 1.

[0029] In this case, Fig. 2 shows a sketch of the THz radiation detector housing; Fig. 3 shows a block diagram of the amplification board used to increase the detection efficiency of THz radiation.

[0030] Information confirming the possibility of implementing the invention

[0031] Fig. 1 shows a diagram of a broadband THz radiation detector. According to this diagram, a thermoelectric element 6 is placed inside a rectangular housing 1, in the center of which an aperture 5 is made for transmitting THz radiation to the surface of a group of thermoelectric branches, sequentially composed of narrow strips of bismuth-antimony and copper.

[0032] Terahertz radiation passes through the input diaphragm and falls on a portion of the thermoelectric branches corresponding to the size of the diaphragm, causing them to heat up and thus creating a temperature gradient along each of the thermoelectric branches, due to which a thermo-EMF arises between the two contacts (electrodes), which is recorded and amplified by means of an amplification board and transmitted to an external voltage measuring device.

[0033] An increase in the length of thermoelectric branches with a corresponding proportional increase in the area of ​​the THz radiation beam incident on them, as well as an increase in the number of such branches with an unchanged beam area, leads to an increase in the detection efficiency due to an increase in the value of the thermo-EMF. Thus, to implement the claimed invention, it is necessary to select the optimal values ​​of the number of branches and their length taking into account the area illuminated by the THz radiation and the optimal width of the thermoelectric branches, ensuring a sufficiently low electrical resistance. It is proposed to use thin films of a bismuth-antimony solid solution as the material from which such thermoelectric branches are made.

[0034] Fig. 2 shows a sketch of the detector housing 1 in the form of a rectangular parallelepiped with mounting threaded holes at the bottom and side 2 for mounting on an optical table using a holder, an interface 3 on the side surface for connecting an external power source, electrical contact interfaces 4 for connecting to an external device for measuring the potential difference. On the front side of the housing in the center there is a rectangular window (diaphragm) 5, limiting the cross-section of terahertz radiation, which falls on the thermoelectric element 6 located behind the window, within the optimal area of ​​its incidence on a group of thermoelectric branches connected to the amplifier board 7, which is located behind the thermoelectric element 6, is powered by an external power source 3 and is connected at the output to the electrical contact interface 4, located on the outer side of the device.Behind the rectangular window 5, on two opposite sides from the thermoelectric element 6, there is a radiator 8, which ensures heat dissipation outside the detector housing 1. The front side of the housing with the diaphragm is closed with a rectangular cover during transportation and storage.

[0035] Fig. 3 shows a block diagram of the amplification board, to the input of which a signal from the sensor (thermoelectric element) 6 is received, passing sequentially through the background signal zeroing and electromagnetic interference filtering units 9 (low-pass filters, LPF), the instrumentation amplifier cascade 10 and the electromagnetic interference filtering unit 11.

Claims

Invention formula 1. A device for detecting continuous and pulsed terahertz radiation in the frequency range from 0.1 to 10 THz, operating on the basis of the photothermoelectric effect, consisting of a sensitive element made on the basis of series-connected thermoelectric materials on a dielectric substrate, and electrodes (conductors) connected to an amplifier board, characterized in that a thin film of a solid solution of bismuth-antimony BiI is used as the thermoelectric material. x Sb x .

2. The device according to item 1, characterized in that the thickness d (nm) of the thin bismuth-antimony film is in the range: 100 < d < 500.

3. The device according to item 2, characterized in that the concentration of antimony x (at.%) is in the range: 5 < x < 17.

4. The device according to item 3, characterized in that the sensitive element is made in the form of an array of thermoelectric branches, the number of which n (pcs.) is determined from the ratio: n > 2.

5. The device according to item 4, characterized in that the width of the thermoelectric branches w (mm) is in the range: 0.01 < w < 3.

0.

6. The device according to item 5, characterized in that the length of the thermoelectric branches 1 (mm) is in the range: 5 < 1 < 50.

7. The device according to item 6, characterized in that the sensitivity of the detector is at least 10 V / 30 mW when using an amplification board.

8. The device according to item 7, characterized in that the equivalent noise power does not exceed the value of 0.15 nW. -1 / 2 .

9. The device according to item 8, characterized in that the response time is no more than 20 μs. 7

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