A low-frequency terahertz transmitting device and its fabrication and application methods

Abstract

This application relates to the field of terahertz emission, specifically providing a low-frequency terahertz emitting device and its fabrication and usage methods. The device includes an excitation material, which is a heterojunction formed by a perovskite layer and a high-resistivity silicon layer. It also includes a first metal layer disposed outside the perovskite layer and a second metal layer disposed outside the high-resistivity silicon layer. During fabrication, a perovskite solution is first spin-coated onto the high-resistivity silicon to form a perovskite layer, and finally, the metal layers are deposited by vapor deposition. During use, a femtosecond laser is incident from one side of the perovskite layer, and a voltage is applied between the first and second metal layers. The applied electric field of this application enhances the interfacial band bending and widens the depletion layer, while simultaneously forming a stable potential gradient in the thickness direction. This makes the transient current change smoother, increases the time constant, and reduces the rate of change of the transient current over time, thereby increasing the proportion of the low-frequency terahertz component and achieving enhanced low-frequency radiation.

Description

Technical Field

[0001] This application relates to the field of terahertz emission, and more specifically, to a low-frequency terahertz emitting device and its preparation and usage methods. Background Technology

[0002] Terahertz waves typically refer to electromagnetic waves with frequencies between 0.1 and 1.0 THz, with the 0.2-0.5 THz range falling in the transition zone between millimeter waves and terahertz, belonging to the Asia-Pacific Hertz band. This band combines the propagation characteristics of millimeter waves with the high resolution advantages of terahertz waves. Compared to higher frequency bands above 1 THz, the 0.2-0.5 THz band exhibits lower absorption loss in air, fewer water vapor absorption peaks, and longer propagation distances. Compared to millimeter wave bands such as 60-100 GHz, the 0.2-0.5 THz band offers a wider usable bandwidth, enabling higher spatial resolution. It has significant application value in fields such as security inspection and penetration imaging, high-resolution radar, industrial non-destructive testing, molecular spectroscopy and fingerprint recognition, and 6G ultra-high-speed wireless communication, especially in applications requiring a balance between penetration capability and information capacity.

[0003] Terahertz emission sources based on the nonlinear crystal optical rectification effect have become one of the most common and widely used optical emission methods. The physical essence of optical rectification is a second-order nonlinear polarization effect. When an ultrashort pulse laser is incident on a crystal with second-order nonlinearity, the square term of the electric field contains a difference frequency term between different frequency components, thus generating terahertz radiation in the low-frequency region. The output spectrum is mainly determined by the pump pulse width, the nonlinear coefficient of the material, and the phase-matching condition. However, the conversion efficiency of the optical rectification mechanism at low frequencies is intrinsically limited by material dispersion and the phase-matching window. In common crystals such as ZnTe and GaP, the phase-matching function is highly sensitive to frequency, and the conversion efficiency below 0.3 THz is usually limited, resulting in insufficient low-frequency energy. In practice, the overall spectrum can be controlled by changing the laser pulse width, adjusting the crystal thickness, and optimizing the tilt angle, but this adjustment will affect the entire spectrum simultaneously, failing to significantly enhance the low-frequency band of 0.2-0.5 THz; the overall enhancement still results in a low proportion of low-frequency components.

[0004] In summary, the 0.2-0.5 THz band accounts for a small proportion of the terahertz spectrum obtained by existing excited materials and methods, resulting in insufficient effective radiated power in this band and difficulty in maintaining a sufficient signal-to-noise ratio, which affects its application in fields such as 6G ultra-high-speed wireless communication and high-resolution radar. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the prior art by providing a low-frequency terahertz transmitting device and its preparation and usage methods, thereby solving the problem that the low-frequency band accounts for a small proportion of the terahertz waves generated by the prior art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This application provides a low-frequency terahertz transmitting device, including an excited material, which is a heterojunction formed by a perovskite layer and a high-resistivity silicon layer, and further includes a first metal layer disposed outside the perovskite layer and a second metal layer disposed outside the high-resistivity silicon layer.

[0007] In this application, a heterojunction is formed between the perovskite layer and the high-resistivity silicon layer, generating a built-in electric field at the interface. The direction of the built-in electric field is from the high-resistivity silicon layer to the perovskite layer. During operation, when a femtosecond laser is incident on the perovskite layer, the photon energy is higher than its bandgap, transiently generating a high density of electron-hole pairs. Under the influence of the built-in electric field of the heterojunction, photogenerated carriers separate and migrate along the thickness direction of the device, forming a transient current. The faster the transient current changes with time, the smaller the corresponding time constant, and the more terahertz high-frequency components there are; conversely, the slower and more gradual the transient current changes with time, the larger the corresponding time constant, and the more concentrated the spectrum is in the low-frequency region.

[0008] The heterojunction interface exhibits band bending and a depletion layer, providing directional separation channels for charge carriers. When a voltage is applied between the first and second metal layers, the applied electric field and the built-in electric field superimpose, resulting in a smoother change in transient current and an increased time constant. Specifically, on one hand, the applied electric field alters the potential distribution at the interface, increasing the degree of band bending. The applied electric field increases the potential barrier height at the interface, causing charge carriers to undergo reflection and re-injection, rather than a single instantaneous crossing. This makes the cross-interface charge transfer process last for several picoseconds or even longer, increasing the slow time constant current component and enhancing low-frequency components. On the other hand, the applied electric field increases the width of the depletion layer, which is beneficial for interface states to participate in the carrier capture and release process. With a wider depletion layer, charge carriers are driven by the electric field over a wider region, increasing the separation path and drift time; simultaneously, the electric field distribution near the interface becomes more gradient-like, which is also beneficial for interface states to participate in the carrier capture and release process. Under the influence of an electric field, the position of the interface state relative to the Fermi level changes, and the capture probability and decapture time constant are redistributed, forming a compensating current component with a longer time constant. This results in a smoother decay of the transient current curve, a reduced rate of change of current, a longer duration, and an increased proportion of low-frequency components. Furthermore, the applied electric field establishes a stable potential gradient along the device thickness, creating a continuous charge pumping channel on the high-resistivity silicon side. When the femtosecond laser generates photogenerated carriers, electrons and holes separate near the interface and migrate in opposite directions. Transient space charge easily accumulates at the interface. With the applied electric field, the silicon side, as a region with low carrier concentration and high resistivity, continuously pulls electrons away from the interface under the influence of the external field, accelerating their movement away and reducing interface charge accumulation, thereby suppressing the weakening of the electric field by space charge. This maintains effective driving for a longer period, slowing down the transient current decay process, extending the current duration, and enhancing the low-frequency components.

[0009] Furthermore, the material of the perovskite layer is a three-dimensional halide organic-inorganic hybrid perovskite material ABX3, where A is an organic cation, B is a metal cation, and X is a halide anion.

[0010] Furthermore, both the first and second metal layers are U-shaped electrodes, disposed at the surface edge regions of the perovskite layer and the high-resistivity silicon layer.

[0011] This application also proposes a method for fabricating a low-frequency terahertz transmitting device, the method comprising the following steps: S1, clean the high-resistivity silicon substrate and perform oxygen plasma treatment; S2, preparation of perovskite precursor solution; S3, a precursor solution is spin-coated onto a high-resistivity silicon substrate and then heat-treated to obtain a perovskite layer. S4, deposit a first metal layer on the side of the perovskite layer away from the high-resistivity silicon substrate, and deposit a second metal layer on the side of the high-resistivity silicon substrate away from the perovskite layer.

[0012] Further, S2 includes dissolving CH3NH3I and PbI2 powders in an organic solvent to obtain a precursor solution.

[0013] Furthermore, the concentration of the precursor solution is 0.1-1 mol / L.

[0014] Furthermore, S3 includes adsorbing a high-resistivity silicon substrate onto a spin coater, adding a precursor solution, and during spin coating, first rotating at a first speed for a first time, and then rotating at a second speed for a second time.

[0015] Furthermore, the second rotational speed is greater than the first rotational speed, and the second time is greater than the first time.

[0016] This application also proposes a method of using a low-frequency terahertz emitting device, which is the same as the method of using the above-mentioned device, wherein the incident laser is incident from one side of the perovskite layer and the terahertz wave is emitted from one side of the high-resistivity silicon layer; at the same time, a voltage is applied between the first metal layer and the second metal layer.

[0017] Furthermore, the first metal layer is connected to the positive terminal of the external power supply, and the second metal layer is connected to the negative terminal of the external power supply.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This application includes a heterojunction structure formed by a perovskite layer and a high-resistivity silicon layer. Upon contact, the heterojunction generates band bending and a depletion layer. Under femtosecond laser irradiation, the heterojunction forms an interfacial transient current, and the change in this transient current generates terahertz radiation. A first metal layer and a second metal layer are used to apply an external electric field. On one hand, the applied electric field increases the degree of band bending at the interface, increasing the potential barrier height for charge transfer at the interface, transforming the cross-interface charge transfer from a single instantaneous crossing into a continuous injection process, and increasing the slow-time-constant current component. On the other hand, the applied electric field widens the depletion region, increasing the drift path of charge carriers within the depletion layer and prolonging their transport time. Simultaneously, the interface states, under electric field modulation, change the trapping and release time constants, forming a compensation current component with a longer timescale. Furthermore, the applied electric field establishes a stable potential gradient on the high-resistivity silicon side, continuously pumping photogenerated charge carriers, suppressing the instantaneous shielding effect of space charge, and maintaining the driving electric field for a longer period. In other words, in this application, the rate of change of transient current with time decreases and the time constant increases, thereby increasing the proportion of terahertz components in the 0.2-0.5 THz low-frequency band and achieving effective enhancement of low-frequency terahertz radiation. Attached Figure Description

[0019] Figure 1 A schematic diagram of a low-frequency terahertz transmitting device provided by the present invention; Figure 2 The comparison results of the time-domain signals of terahertz waves generated under conditions of no external bias voltage and with applied external bias voltage obtained by the method of using a low-frequency terahertz transmitting device provided by the present invention; Figure 3 for Figure 2 The frequency domain spectrum corresponding to the terahertz wave time-domain signal is shown below; Figure 4 The terahertz radiation frequency domain spectrum generated by the method in Example 4; Figure 5 The terahertz radiation frequency domain spectrum generated by the method in Example 5.

[0020] Icons: 1-First metal layer; 2-Perovskite layer; 3-High-resistivity silicon layer; 4-Second metal layer. Detailed Implementation

[0021] To make the implementation process of this invention clearer, a detailed description will be provided below in conjunction with the accompanying drawings.

[0022] Example 1: This invention provides a low-frequency terahertz transmitting device, such as... Figure 1 As shown, from top to bottom, the device sequentially includes a first metal layer 1, a perovskite layer 2, a high-resistivity silicon layer 3, and a second metal layer 4. The perovskite layer 2 and the high-resistivity silicon layer 3 form a heterojunction, which is the excited material and generates terahertz radiation under femtosecond laser excitation. The material of the perovskite layer 2 is a three-dimensional halide organic-inorganic hybrid perovskite material ABX3, where A is an organic cation, such as MA. + FA + B is a metal cation, such as Pb. 2+ Sn 2+ X is a halide anion, such as Cl. - ,Br - I -ABX3 possesses a high optical absorption coefficient, enabling the generation of high-density photogenerated carriers under femtosecond laser irradiation. Simultaneously, its long carrier lifetime and slow nonradiative recombination dynamics allow carriers to participate in transport over a longer timescale, increasing the slow time constant current component. The heterojunction formed by perovskite and high-resistivity silicon generates a built-in electric field, which facilitates directional carrier separation and continuous transport, resulting in smoother transient current changes, increased low-frequency component proportion, and enhanced terahertz signals in the low-frequency band. The preferred substrate is MAPbI3. MAPbI3 is low-cost and easy to prepare, and has a high absorption coefficient, allowing photogenerated carriers to be generated primarily near the interface, thus enhancing the interface modulation effect. It also has a long carrier lifetime and slow nonradiative recombination kinetics, enabling a continuous injection process of carriers under interface barrier modulation, extending the current decay time and enhancing low-frequency performance. Forming a type II heterojunction with high-resistivity silicon, both the barrier height and depletion layer width can be modulated when a voltage is applied, transforming the cross-interface charge transfer from a fast transient process to a continuous transport process, increasing the slow time constant current component, and enhancing low-frequency terahertz radiation. The high-resistivity silicon layer 3 is n-type doped with a resistivity of 5000 Ω·cm, determining the direction of the built-in electric field, forming a built-in electric field pointing from the high-resistivity silicon layer 3 to the perovskite layer 2. The low doping concentration ensures the formation of a relatively wide depletion layer, enhancing the interface electric field modulation capability; ensuring that the applied voltage acts sufficiently and effectively at the heterojunction interface, improving the interface barrier modulation efficiency, and making the slow timescale transport process more prominent.

[0023] Furthermore, the thickness of the perovskite layer 2 is 50-100 nm, which ensures that photogenerated carriers are generated near the heterojunction interface, enhancing the interface dominance effect. If the perovskite layer 2 is too thick, it will absorb most of the pump light, causing most photogenerated carriers to be generated in the perovskite material far from the interface, weakening the interface effect and suppressing the enhancement of low-frequency components; if the perovskite layer 2 is too thin, it will be discontinuous and not dense, leading to leakage. The thickness of the high-resistivity silicon layer 3 is 500 μm. On the one hand, the high-resistivity silicon layer 3 is a crucial propagation medium for terahertz radiation coupling from the device outwards. If the thickness is too thin, the propagation distance of the terahertz wave in the silicon is insufficient, failing to form a stable radiation exit surface, leading to reduced radiation efficiency. An excessively thin silicon layer weakens the stability of the device's potential distribution along the thickness direction, making the applied electric field more susceptible to interface charges and surface effects, reducing the field's controllability near the heterojunction, and weakening its modulation of transient current dynamics. Furthermore, an excessively thin high-resistivity silicon layer 3 enhances surface scattering and reflection, causing some terahertz waves to be reflected or interfered with at the interface, reducing output intensity. The high-resistivity silicon layer 3 has a thickness of 500 μm, ensuring the device's mechanical stability while providing sufficient propagation and exit paths for the terahertz wave and maintaining a stable electric field distribution, thus facilitating the effective generation and output of terahertz signals.

[0024] The overall device adopts a square structure, which is conducive to forming a uniform and stable electric field distribution, thereby enhancing terahertz signals in the low-frequency band. The square structure has symmetry in four directions, enabling a relatively uniform potential boundary condition to be formed between the first metal layer 1 and the second metal layer 4. The externally applied electric field is more stable in the thickness direction of the device, reducing the concentration and distortion of the electric field in the edge region, and forming a uniform energy band bending and depletion region structure at the heterojunction interface, thereby making the interface barrier modulation more consistent. The stable and uniform electric field distribution can promote continuous injection across the interface, making the transient current change more gentle and increasing the time constant, thus increasing the proportion of terahertz components in the low-frequency band. In addition, the square structure has clear boundaries and easy-to-control dimensions, facilitating stable spot coverage and repeated measurement in terahertz spectroscopy testing, and improving the stability and repeatability of low-frequency signal measurement.

[0025] The materials of the first metal layer 1 and the second metal layer 4 are gold, which has excellent chemical stability and is not easily oxidized, ensuring the stability of the heterojunction interface; achieving good ohmic contact to ensure that the externally applied electric field can be efficiently applied to both ends of the perovskite and high-resistance silicon heterojunction. The thickness is 50 - 100 nm. If the metal layer is too thin, the connection area is discontinuous and the adhesion is weak, and it is easily damaged and peeled off during subsequent process treatment or testing; if the thickness is too thick, the material cost increases, and the too long evaporation time will affect the perovskite layer 2. In order not to affect the irradiation of incident light in the middle region of the perovskite layer 2 and the emission of terahertz radiation in the middle region of the high-resistance silicon layer 3, the shapes of the first metal layer 1 and the second metal layer 4 are in the shape of a rectangle with a hollow center, and are arranged in the surface edge regions of the perovskite layer 2 and the high-resistance silicon layer 3, with the outer side more than 1 mm away from the edge, which can avoid the edge of the perovskite film. In the spin-coating process, the edge region is uneven, thus ensuring good ohmic contact between the metal and the semiconductor. The widths of the four sides of the rectangle with a hollow center are the same, and the width is 1.5 - 2.5 mm, preferably 2 mm, so as to facilitate the formation of a uniform electric field distribution, increase the electric field strength in the central excited region, make the externally applied voltage act more effectively on the heterojunction depletion layer, enhance the interface barrier modulation ability, extend the carrier drift and relaxation time, thereby increasing the slow time constant current component and enhancing the terahertz radiation in the low-frequency band. Preferably, the thickness of the second metal layer 4 is greater than that of the first metal layer 1. When the second metal layer 4 is thicker than the first metal layer 1, a difference is formed in the conductivity and potential constraint ability of the electrodes on the upper and lower sides of the device. On the side of the thicker second metal layer 4, the potential distribution is more stable and the transverse potential gradient is smaller. The electric field lines tend to be distributed along the thickness direction from the perovskite side to the silicon side, rather than bending and diffusing on the surface. This increases the proportion of the electric field component in the thickness direction in the heterojunction region, makes the interface barrier modulation and depletion region expansion more concentrated in the vertical direction, promotes continuous transport across the interface and the formation of slow time constant current components, and weakens the sharp change of the transient current, thereby increasing the proportion of terahertz components in the low-frequency band and achieving low-frequency enhancement.

[0026] Furthermore, the first metal layer 1 and the second metal layer 4 adopt a thickness gradient structure that gradually increases in thickness from the inside out. The inner edge near the middle region is thinner, and the thickness gradually increases radially outward. This reduces the sheet resistance and contact resistance of the outer power supply path, allowing the applied voltage to be applied more fully and stably to the heterojunction and its depletion layer, avoiding the potential gradient caused by electrode voltage drop. This results in a more uniform potential gradient in the thickness direction and an increased proportion of the electric field component in the thickness direction. The effect of the applied electric field is stronger, and the time constant of the transient current is larger, thereby enhancing the low-frequency intensity. At the same time, the thicker outer layer can also disperse the current density, reduce local heating and edge electric field concentration, improve the stability of the device under bias, and ensure the repeatability of the low-frequency enhancement effect.

[0027] Furthermore, before depositing the gold electrodes of the first metal layer 1 and the second metal layer 4, a titanium layer of approximately 5 nm thickness is deposited on the surfaces of the perovskite layer 2 and the high-resistivity silicon layer 3, followed by gold deposition to form a Ti / Au composite electrode. Titanium enhances the adhesion between the metal electrode and the perovskite or high-resistivity silicon surface, reduces contact resistance, decreases the additional contact barrier at the interface, and reduces ineffective voltage loss at the contact interface. This allows the applied bias voltage to act more fully on the interface and depletion region of the perovskite and high-resistivity silicon heterojunction, improving the efficiency of interface band bending and barrier modulation. Simultaneously, the improved contact stability reduces local hotspots and potential drift, allowing slow processes such as cross-interface continuous injection, interface state trapping and release, and high-resistivity silicon-side pumping to occur more fully, thereby enhancing the low-frequency terahertz signal.

[0028] Example 2: Example 1: The fabrication method of the device includes the following steps: S1, clean the high-resistivity silicon substrate and perform oxygen plasma treatment.

[0029] The high-resistivity silicon substrate underwent cleaning and pretreatment. Specifically, the substrate was ultrasonically cleaned sequentially with deionized water and organic solvents to remove surface contaminants. Then, it was ultrasonically cleaned for 15 minutes each with deionized water, acetone, and alcohol. After cleaning, the substrate was treated with oxygen plasma. Specifically, the surface of the perovskite layer 2 to be spin-coated was treated with oxygen plasma. The cleaned high-resistivity silicon substrate was placed in the reaction chamber of an oxygen plasma cleaner, with the treatment side facing upwards. A vacuum was drawn to below 60 Pa, and high-purity oxygen was introduced as the treatment gas. Oxygen plasma was generated using radio frequency excitation for 20 minutes. The oxygen plasma contains various highly reactive substances. Under ultraviolet radiation, the gaseous substances in the oxygen plasma interact with the material surface, decomposing organic contaminants into small molecules such as CO2 and H2O, which are then removed by the vacuum system. After removing contaminants, the substances in the oxygen plasma react with free radicals generated on the substrate surface, producing hydrophilic groups and increasing hydrophilicity. The active particles of the plasma interact with the material surface. Oxygen plasma deeply cleans the substrate surface and removes organic contaminants; it increases the hydrophilicity and surface energy of the substrate surface, thereby improving the wettability and adhesion of the perovskite solution, ensuring more uniform and dense film deposition, and improving the quality of the film and the performance of the final device.

[0030] S2, to prepare a perovskite precursor solution.

[0031] CH3NH3I and PbI2 powders were dissolved in an organic solvent with a molar ratio of 1:1. The organic solvent was N,N-dimethylformamide. The solution was stirred for 4-8 hours until completely dissolved to obtain a MAPbI3 precursor solution. The concentration of the precursor solution was 0.1-1 mol / L. The thickness of the perovskite film was mainly determined by the precursor concentration and spin-coating speed. This concentration range of precursor solution ensured the formation of a continuous, dense, and moderately thick perovskite layer 2, preventing leakage. Furthermore, the good crystal quality and uniformity resulted in a uniform heterojunction interface, ensuring a uniform spatial distribution of the electric field modulation. The perovskite layer 2 prepared at this concentration had a light absorption length close to that of MAPbI3 for 400 nm pump light, allowing photogenerated carriers to reach the heterojunction interface with only a very short diffusion distance and time after generation, reducing diffusion losses and enhancing the modulation effect of the transient current at the interface, thereby strengthening the low-frequency components. Then, the film is filtered through a 0.22 μm polytetrafluoroethylene filter to remove particulate impurities. The 0.22 μm pore size can trap particles in the precursor solution that have a significant impact on the film quality. Large particles can disrupt the continuity of the film, cause leakage, weaken the electric field's ability to control charge carriers, and introduce strong recombination centers, consuming photogenerated charge carriers.

[0032] S3. Spin-coat the precursor solution on the high-resistivity silicon substrate, and obtain the perovskite layer 2 after heat treatment.

[0033] Adsorb the high-resistivity silicon substrate on the spin coater, and drop the precursor solution obtained in Step 2. The dropping volume is about 30 μL. The spin-coating process adopts a two-step spin-coating process: first rotate at the first rotation speed for the first time, and then rotate at the second rotation speed for the second time. The first rotation speed is 1000 r / min, and the first time is 10 s; the second rotation speed is 5000 r / min, and the second time is 30 s. The low-speed rotation in the first step mainly realizes the preliminary spreading and uniform distribution of the precursor solution on the substrate, and the high-speed rotation in the second step is used to precisely control the final film thickness and spin out the excess solution to obtain a thin and uniform liquid film. A dense, continuous and low-defect film is the basis for electrical regulation, and an appropriate thickness ensures that there are enough photo-generated carriers to transport to the interface to participate in the regulated slow process.

[0034] Preferably, 300 μL of anti-solvent is dropped during the second-stage spin-coating process during spin-coating to promote rapid crystal nucleation. The anti-solvent is anisole, which rapidly extracts the solvent during the spin-coating process, reduces the solubility, promotes the perovskite precursor to be rapidly supersaturated and form uniform crystal nuclei, thereby promoting rapid crystal nucleation and dense crystallization. After spin-coating, place the sample on a heating table at 100 °C for heat treatment for 15 min; completely remove the residual solvent, induce and promote the growth of perovskite crystals, and improve the film densification.

[0035] More preferably, after spin-coating, a vertical electrostatic field along the normal direction of the substrate is applied to the substrate and the perovskite layer 2. A voltage can be applied to the parallel plate electrodes to generate a parallel electric field. A vertical electric field is established between the high-resistivity silicon substrate and the perovskite surface. The direction of the electric field points from the side of the high-resistivity silicon substrate to the side of the perovskite layer surface, which is consistent with the direction of the thickness-direction electric field formed by the reverse bias during device operation. Apply the electrostatic field immediately after spin-coating, and maintain it for at least 30 - 60 s, or it can also continue until the heat treatment ends. The intensity of the electric field is 10 2 -10 4 V / m. The vertical electrostatic field can regulate the orientation of polar precursor ions and the direction of crystal nucleus growth, making the perovskite grains more inclined to grow along the thickness direction, forming a columnar vertically oriented grain structure, thereby reducing carrier scattering caused by lateral grain boundaries and random orientations. The perovskite layer 2 with a vertical orientation structure enables photo-generated carriers to transport more smoothly in the thickness direction to the perovskite and high-resistivity silicon heterojunction interface, and it is easier to form a continuous injection and slow relaxation process under the action of interface barrier modulation, enhancing the slow time-constant current component and making the transient current decay more gently, thereby further improving the enhancement effect of low-frequency terahertz signals.

[0036] S4, deposit a first metal layer 1 on the side of the perovskite layer 2 away from the high-resistivity silicon substrate, and deposit a second metal layer 4 on the side of the high-resistivity silicon substrate away from the perovskite layer 2.

[0037] A first metal layer 1 is deposited on the surface of a perovskite material by vapor deposition, and a second metal layer 4 is deposited on the surface of a high-resistivity silicon material by vapor deposition. The first metal layer 1 and the second metal layer 4 are arranged in a U-shape at the edge of the device. The U-shape structure is formed by aligning the four edges with a mask and vapor deposition in one step. The vapor deposition is performed in a high vacuum environment with a density of 1×10⁻⁶. -4 Up to 1×10 -5 Pa; the evaporation rate is first 0.1 Å / s for 10 nm slow evaporation, and then 1 Å / s fast evaporation to the specified thickness. The slow evaporation first is to form a uniform, low-damage interface buffer layer; the fast evaporation later is to improve efficiency and complete the thick film deposition.

[0038] Example 3: The device in Example 1 is used as follows: A 400 nm femtosecond laser is incident from one side of the perovskite layer 2 at a 40° tilt angle, ensuring the entire laser spot irradiates the perovskite surface, generating a high density of photogenerated carriers within the perovskite layer 2; the terahertz wave exits from the high-resistivity silicon layer 3. The photon energy of the 400 nm femtosecond laser is greater than the material bandgap, thus generating carriers. Based on the dipole radiation model, oblique incident excitation allows the generated terahertz radiation to form an angle with the material surface, which is more conducive to the collection of terahertz radiation. The laser spot is circular to ensure complete irradiation of the perovskite layer 2, and the optical power is 6 mW, ensuring both a strong terahertz signal and avoiding material damage. The time-domain and frequency-domain signals of the emitted terahertz wave are as follows: Figure 2 and Figure 3 The curve is shown under the condition of 0 V.

[0039] Simultaneously, an external voltage is applied to the first metal layer 1 and the second metal layer 4. The first metal layer 1 is connected to the positive terminal of the external power supply, and the second metal layer 4 is connected to the negative terminal of the external power supply. The applied voltage is a reverse bias, and the direction of the applied electric field is the same as the direction of the built-in electric field of the heterojunction. In this application, the applied voltage ranges from -5 V to -40 V. By changing the magnitude of the applied voltage, the resulting terahertz signal is as follows: Figure 2 and Figure 3 As shown. Among them, Figure 2The changes in the time-domain waveform of the terahertz signal generated by the device under no voltage and different reverse biases (-10 V, -20 V, -30 V, -40 V) are shown. At no bias (0 V), both the rising and falling edges of the terahertz time-domain signal are steep, and the main peak width is narrow, indicating a large transient current change rate. When an external voltage is applied, a significant widening of the main peak waveform is observed, and the time-domain signal decay process slows down. As the voltage increases, the overall signal width increases significantly, and the waveform becomes smoother, exhibiting oscillating characteristics with a tail. Correspondingly, Figure 3 for Figure 2 The frequency domain spectra of the signals in each time domain are shown. Under 0 V conditions, the main peak of the spectrum is located near 1 THz, and the spectrum distribution is uniform. As the applied voltage increases, the intensity of the 0.2-0.3 THz band increases significantly, and the energy proportion of the low-frequency part gradually increases. At -20 V, -30 V, and -40 V, the peak position of the low-frequency peak is the same. After applying an external voltage, the generated terahertz radiation signal changes in both the time domain signal and the spectral structure. When a reverse bias voltage is applied, the 0.2-0.3 THz band is enhanced; that is, the external electric field in the same direction does indeed increase the intensity of the low-frequency signal.

[0040] Furthermore, when applying voltage, a small forward pre-bias is applied first, followed by switching to a reverse working bias. Before femtosecond laser irradiation, a small forward pre-bias is applied to the first metal layer 1 and the second metal layer 4, for example, a forward bias of 1-2 V for 100 ms-1 s; then the forward pre-bias is removed, and the reverse working bias is switched within 1 μs-100 ms. In this way, on the one hand, the small forward pre-bias redistributes the original fixed space charge, accumulated charge, and some deep trap occupancy states at the interface, reducing interface charge pinning and local shielding effects, allowing the subsequent reverse bias to act more fully on the interface barrier and depletion region; on the other hand, the small amplitude of the forward pre-bias avoids the injection of a large number of fast-process carriers and additional heat accumulation caused by strong forward conduction, only mildly adjusting the interface state occupancy distribution, allowing some deep traps to be released and shallow traps to re-participate in the subsequent trapping and release processes. In this way, after switching to reverse working bias, it is easier to form a stable continuous injection and slow time constant compensation current component, making the transient current tail more obvious and the time constant larger, thereby further improving the enhancement effect and repeatability of low-frequency terahertz signals.

[0041] Example 4: The difference from Example 3 is that no external voltage is applied to the first metal layer 1 and the second metal layer 4 in this example, and external continuous light is added for irradiation. The wavelength of the continuous light is 633 nm, and the vertical irradiation completely overlaps with the 400 nm pump light. The light intensity is adjusted by adding an attenuator in the optical path, with an adjustable range of 0-30 mW.

[0042] like Figure 4 As shown, this is the terahertz spectrum generated under conditions of no external voltage and only continuous light illumination. It can be observed that the overall terahertz amplitude changes somewhat, showing a slight increase at 5 mW. As the optical power continues to increase, the overall amplitude gradually decreases, but the spectral distribution characteristics remain essentially unchanged, with no significant enhancement in the low-frequency region. In other words, when only continuous light is applied, the overall amplitude of the generated terahertz radiation changes, but its spectral distribution characteristics remain unchanged, and it does not enhance the low frequencies.

[0043] Example 5: In this embodiment, a voltage was applied to the first metal layer 1 and the second metal layer 4, and a continuous optical field as described in Embodiment 3 was established. The resulting signal is as follows: Figure 5 As shown, when only voltage is applied, the spectral structure changes, with a significant enhancement in the 0.2-0.3 THz low-frequency band. However, when continuous illumination is introduced while applying the same voltage, the previously enhanced 0.2-0.3 THz low-frequency component is significantly weakened, and the overall spectral shape approaches the spectral shape under no bias (0 V) conditions. Figure 3 compared to, Figure 5 The reduced intensity of low-frequency terahertz radiation generated by continuous light indicates that continuous light suppresses the terahertz spectrum modulation effect caused by external bias voltage. This is because continuous light illumination generates steady-state carrier accumulation in the device, forming a space charge distribution, which in turn shields the built-in and applied electric fields to a certain extent, weakening the ability of the applied bias voltage to regulate the interface barrier and carrier dynamics. Specifically, when a heterojunction is simultaneously irradiated with continuous light in addition to a femtosecond pulse, steady-state photogenerated carriers will form in the heterojunction, which weaken the low-frequency enhancement effect of the applied electric field. On the other hand, free electrons and holes generated by continuous light accumulate near the interface and depletion layer, forming additional space charge. The space charge field formed by this additional space charge shields the built-in and applied electric fields, reducing the effective electric field acting on the depletion layer, decreasing the interface band bending and barrier modulation capabilities, and weakening the continuous injection and slow timescale transport processes that originally depended on a strong electric field. On the other hand, steady-state photogenerated carriers fill the depletion layer, causing the depletion layer width to shrink, the main distribution area of ​​the electric field to decrease, the modulation amplitude of the interface barrier to decrease, and the carrier transport and relaxation time to be shortened, suppressing the slow time constant current component. Furthermore, continuous light continuously fills the interface state, causing the state to tend towards a quasi-steady state. The trapping and release processes no longer exhibit significant delayed release currents, and the slow tail current component weakens. This makes the transient current closer to a fast, sharp pulse form, reducing the time constant and decreasing the proportion of low-frequency components. This indicates that the low-frequency enhancement in this application originates from the electric field's regulation of the interface dynamics, rather than a simple increase in the number of carriers.

[0044] In addition, the present invention can achieve spectrum modulation through electrical means without changing the physical structure of the device or introducing complex resonant units. The device has a simple structure and flexible modulation method, which is conducive to the integration and practical application of the device.

[0045] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-frequency terahertz emitting device, the device comprising an excited material, characterized in that: The excited material is a heterojunction formed by a perovskite layer and a high-resistivity silicon layer, and also includes a first metal layer disposed outside the perovskite layer and a second metal layer disposed outside the high-resistivity silicon layer.

2. The low-frequency terahertz transmitting device according to claim 1, characterized in that: The material of the perovskite layer is a three-dimensional halide organic-inorganic hybrid perovskite material ABX3, wherein A is an organic cation, B is a metal cation, and X is a halide anion.

3. The low-frequency terahertz transmitting device according to claim 2, characterized in that: Both the first metal layer and the second metal layer are U-shaped electrodes, disposed at the surface edge regions of the perovskite layer and the high-resistivity silicon layer.

4. A method for fabricating a low-frequency terahertz transmitting device, characterized in that: The preparation method includes the following steps: S1, clean the high-resistivity silicon substrate and perform oxygen plasma treatment; S2, preparation of perovskite precursor solution; S3, spin-coating the precursor solution onto a high-resistivity silicon substrate, and obtaining a perovskite layer after heat treatment; S4, deposit a first metal layer on the side of the perovskite layer away from the high-resistivity silicon substrate, and deposit a second metal layer on the side of the high-resistivity silicon substrate away from the perovskite layer.

5. The method for fabricating a low-frequency terahertz transmitting device according to claim 4, characterized in that: S2 involves dissolving CH3NH3I and PbI2 powders in an organic solvent to obtain the precursor solution.

6. The method for fabricating a low-frequency terahertz transmitting device according to claim 5, characterized in that: The concentration of the precursor solution is 0.1-1 mol / L.

7. The method for fabricating a low-frequency terahertz transmitting device according to claim 6, characterized in that: S3 includes adsorbing the high-resistivity silicon substrate onto a spin coater, adding the precursor solution dropwise, and during spin coating, first rotating at a first speed for a first time, and then rotating at a second speed for a second time.

8. The method for fabricating a low-frequency terahertz transmitting device according to claim 7, characterized in that: The second rotational speed is greater than the first rotational speed, and the second time is greater than the first time.

9. A method of using a low-frequency terahertz transmitting device, characterized in that: The method is a way of using the device according to any one of claims 1-3, wherein the incident laser is incident from one side of the perovskite layer and the terahertz wave is emitted from one side of the high-resistivity silicon layer; at the same time, a voltage is applied between the first metal layer and the second metal layer.

10. The method of using the low-frequency terahertz transmitting device according to claim 9, characterized in that: The first metal layer is connected to the positive terminal of the external power supply, and the second metal layer is connected to the negative terminal of the external power supply.

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