An active electrically tunable terahertz device based on metamaterial structure

Abstract

The application provides an active electrically-adjusted terahertz device based on a metamaterial structure, and belongs to the technical field of terahertz technology.The device structure comprises a metamaterial layer, a substrate layer, a metal plate and metal electrodes; the metamaterial layer is composed of a periodic array structure; the substrate layer is a III-V semiconductor with a negative differential resistance effect; the metal plate is made on the lower surface of the substrate; and the two metal electrodes are made on the upper surface of the substrate; a high bias voltage is applied to the semiconductor substrate through the two metal electrodes to generate a strong transverse electric field inside the semiconductor substrate, cause the negative differential resistance effect of the semiconductor material, change the material properties of the semiconductor substrate, thereby affecting the resonant frequency of the device, and form an active electrically-adjusted terahertz metamaterial device.

Description

Technical Field

[0001] This invention relates to the design of an actively electrically controlled terahertz device based on a metamaterial structure, belonging to the technical field of terahertz device manufacturing. Background Technology

[0002] Terahertz waves are electromagnetic waves with frequencies between 0.1 and 10 THz, falling between the microwave and infrared bands on the electromagnetic spectrum. Compared to microwave technology, terahertz technology offers higher resolution; compared to optical wave technology, terahertz waves have lower energy and stronger penetrating power, making them widely applicable in radar, security inspection, and imaging. However, the development of terahertz technology is somewhat limited because many natural materials exhibit very weak electromagnetic responses to terahertz waves. Metamaterials, as artificial electromagnetic materials composed of periodically or non-periodically arranged metallic structures, can effectively control the amplitude, phase, polarization, and propagation mode of terahertz waves, enabling the realization of many terahertz functional devices, such as absorbers, optical switches, and polarization devices.

[0003] Currently, much research both domestically and internationally focuses on actively tunable terahertz metamaterial devices. There are generally three ways to realize actively tunable terahertz metamaterial devices. The first is to integrate nonlinear components (such as Gunn diodes, Schottky diodes, and varactor diodes) or nonlinear materials at the opening of an open-circuit resonator. The second is based on mechanically reconfigurable metamaterials using micro / nano-electromechanical systems, where the shape or arrangement of structural units is changed through mechanical control. The third is to fabricate metamaterials or metamaterial substrates using materials whose dielectric properties are tunable under external forces (such as light, electricity, and heat), such as semiconductors, liquid crystals, ferroelectric materials, and phase change materials.

[0004] As mentioned above, there are various ways to realize actively tunable metamaterial devices, but so far, no method has been developed to dynamically electrically control the electromagnetic properties of metamaterial devices using the negative differential resistance effect of group III-V semiconductors (such as GaAs, GaN, InP, etc.). The metamaterial terahertz device proposed in this invention utilizes the negative differential resistance effect of group III-V semiconductors to modulate the electromagnetic properties of the device, providing a novel approach for realizing actively tunable metamaterial terahertz devices. Summary of the Invention

[0005] Technical Problem: The purpose of this invention is to provide an actively electrically tunable terahertz device based on a metamaterial structure. By applying a high bias lateral voltage to a III-V group semiconductor substrate (equivalent to forming a Gunn diode), a negative differential resistance effect is generated inside the semiconductor. Due to the electron transfer mechanism, the distribution of carrier concentration, mobility, and effective mass within the substrate will change, thereby altering the resonant characteristics of the device and forming a voltage-tunable active terahertz metamaterial device.

[0006] Technical solution: The present invention provides an actively electrically controlled terahertz device based on a metamaterial structure, which is achieved through the following technical means.

[0007] The device consists of a metamaterial layer, a substrate layer, a first electrode, a first highly doped semiconductor layer, a second electrode, a second highly doped semiconductor layer, and a metal plate. The metamaterial layer is disposed on top of the substrate layer, and the first highly doped semiconductor layer and the second highly doped semiconductor layer are disposed on the two symmetrical sides of the substrate layer, respectively. The first electrode is disposed on the first highly doped semiconductor layer, and the second electrode is disposed on the second highly doped semiconductor layer. The metamaterial layer, the first electrode, and the second electrode are on the same plane, and the metal plate is disposed below the substrate layer.

[0008] The structural units are arranged periodically on the substrate, with the first electrode and the second electrode located on either side of the structural unit.

[0009] The structural unit of the metamaterial layer is one of a square, an open resonant ring, or a circular ring.

[0010] The substrate is a semiconductor material with a negative differential resistance effect.

[0011] The metal plate is fabricated on the lower surface of the semiconductor substrate; the thickness of the metal plate is greater than the skin depth through which electromagnetic waves propagate, so as to ensure that the transmittance of the device is 0.

[0012] The structural unit, the first electrode, the second electrode, and the metal plate are made of one of the following materials: gold, silver, copper, and aluminum.

[0013] The first electrode and the second electrode form ohmic contacts with the corresponding first highly doped semiconductor layer and the second highly doped semiconductor layer below them.

[0014] The substrate, the first highly doped semiconductor layer, and the second highly doped semiconductor layer are made of gallium arsenide, gallium nitride, or indium phosphide. A high bias voltage is applied to the substrate through the first and second electrodes. At this time, the first and second electrodes and the substrate form a Gunn diode, generating a negative differential resistance effect in the substrate. Due to the electron transfer mechanism, the distribution of carrier concentration, mobility, and effective mass in the substrate will change, thereby changing the resonant characteristics of the device.

[0015] The operating mode of the Geng diode is one of the following: ideal mode, dipole domain transit time mode, electron accumulation domain mode, confined space charge accumulation mode, or quenched dipole layer mode.

[0016] Beneficial Effects: The actively electrically controlled terahertz device based on metamaterial structures proposed in this invention utilizes the negative differential resistance effect of group III-V semiconductors to alter the device's absorption characteristics, providing a novel approach for realizing active metamaterial terahertz devices. Furthermore, compared to dynamic control using methods such as light, heat, and magnetism, voltage-based control is easier to achieve, requires no complex equipment or experimental conditions, and is more convenient to use. Attached Figure Description

[0017] Figure 1 This is a three-dimensional schematic diagram (top) of the active electrically controlled terahertz device structure based on metamaterial structure described in this invention;

[0018] Figure 2 This is a three-dimensional schematic diagram (bottom) of the active electrically controlled terahertz device structure based on metamaterial structure described in this invention;

[0019] Figure 3 This is a two-dimensional top view of the actively electrically controlled terahertz device based on metamaterial structure described in this invention;

[0020] Figure 4 This is a two-dimensional bottom view of the actively electrically controlled terahertz device based on metamaterial structure described in this invention.

[0021] Figure 5 This is the absorption characteristic curve of the device under ideal mode with or without voltage applied.

[0022] The figure includes: structural unit 1, substrate layer 2, first electrode 3, first highly doped semiconductor layer 4, second electrode 5, second highly doped semiconductor layer 6, and metal plate 7. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0024] Example 1:

[0025] like Figure 1 As shown, the actively electrically controlled terahertz device based on a metamaterial structure described in this invention consists of a metamaterial layer, a substrate layer, a metal plate, and metal electrodes. Figure 3 As shown, the metamaterial layer consists of periodically arranged structural units. The substrate layer is a semiconductor material with negative differential resistance. Figure 2 and Figure 4 As shown, a metal plate is fabricated on the lower surface of a semiconductor substrate. Two metal electrodes are fabricated on the upper surface of the semiconductor substrate. Figure 1 As shown in the striped pattern area, there is a highly doped semiconductor layer under the pattern corresponding to the two electrodes to enable the two electrodes to form an ohmic contact with the substrate layer.

[0026] The structural units of the metamaterial layer can adopt a square structure, split-ring resonator, ring structure, etc. In this embodiment, the square structure is preferably used.

[0027] The materials of the metamaterial layer, metal plate and metal electrode can adopt gold, silver, copper, aluminum, etc. In this embodiment, gold is preferably used.

[0028] In this embodiment, it is preferred that the period of the metamaterial structural unit is 50 um, the side length is 36 um, the thickness is 150 nm, the thickness of the substrate layer is preferably 8 um, and the substrate doping concentration is 1×10 16 cm -3 , and the thickness of the metal plate is preferably 2 um.

[0029] Tuning the material properties of the semiconductor substrate is a means of dynamically controlling the electromagnetic response of the metamaterial; in this embodiment, the substrate layer uses a III-V semiconductor, and the material properties of the semiconductor are modulated based on the negative differential resistance effect. The semiconductor material is one of gallium arsenide, gallium nitride, and indium phosphide. In this embodiment, gallium arsenide is preferably used; a high bias voltage is applied to the gallium arsenide substrate through two electrodes; at this time, the two electrodes and the gallium arsenide substrate form a Gunn diode; the Gunn diode based on the negative differential resistance effect has five working modes: ideal mode, dipole domain transit time mode, electron accumulation domain mode, limited space charge accumulation mode, quenched dipole layer mode. In this embodiment, assuming that there are no defects and inhomogeneities in the semiconductor, the ideal mode will be generated at this time; in the ideal mode, the high electric field is uniformly distributed throughout the semiconductor. Therefore, it can be considered that the movement of carriers everywhere in the semiconductor is the same, and the material properties everywhere in the semiconductor are also the same, and no oscillating current will be generated; in this ideal mode, the electrons in the central valley of the semiconductor gain enough energy to jump to the satellite valley, which will cause the electron mobility of the semiconductor material to become smaller, the effective mass of electrons to become larger, and the real part of the dielectric constant to increase, thereby causing the resonance frequency of the device to shift to the red. The change in the resonance intensity of the device is mainly affected by the impedance matching degree. The material properties of the semiconductor material change with the voltage, which will affect the equivalent impedance of the device.

[0030] As Figure 5 shown is the absorption characteristic curve of the device with (without) voltage applied. Among them, V0 = 0 < V1, and V1 can excite all electrons to the high-energy valley. It can be seen from the curve that after the voltage is applied, the resonance frequency of the device decreases and the resonance intensity increases.

[0031] Therefore, in the ideal mode, by applying different magnitudes of transverse voltage, the time-invariant regulation of the resonance frequency and resonance amplitude of the metamaterial device can be achieved. However, this mode has very high requirements for the contact between the semiconductor material and the electrode, so it is very difficult to achieve. In practice, the dipole domain transit time mode is more likely to occur in this device.

[0032] Example 2:

[0033] The following changes were made to this embodiment compared to Embodiment 1:

[0034] In reality, semiconductor samples always contain various defects and impurities, which typically generate charge domains near the cathode due to fluctuations in carrier concentration. The device described in this invention more readily generates a dipole domain transit time mode. In this mode, dipole domains, consisting of an electron accumulation layer and an electron depletion layer, are generated near the cathode. After being generated at the cathode, these dipole domains grow continuously as they move towards the anode, eventually being absorbed by the anode. The cycle then repeats, generating an oscillating current.

[0035] Dipole domains consist of an electron accumulation layer and an electron depletion layer. When dipole domains are first generated at the cathode, the electron concentration in the electron accumulation layer increases, mobility decreases, and its layer width is relatively small, so its effect can be ignored. Similarly, the electron concentration and mobility decrease in the electron depletion layer, and its layer width is also relatively small, so its effect can also be ignored. In the region between the cathode and the electron accumulation layer, electron concentration and mobility are uniform, and the electric field is low, resulting in high mobility. In the region between the electron accumulation layer and the electron depletion layer, electron concentration and mobility are uniform, and the electric field is high, resulting in low mobility. In the region between the electron depletion layer and the anode, electron concentration and mobility are uniform, and the electric field is low, resulting in high mobility. Therefore, compared to semiconductor materials without an applied electric field, semiconductors with a high bias voltage exhibit reduced overall electron mobility and increased effective mass. This leads to a larger real part of the dielectric constant, which affects metamaterial devices, causing a redshift in the resonant frequency.

[0036] As the dipole domains continue to move toward the anode, the region between the cathode and the electron accumulation layer gradually lengthens, the region between the electron accumulation layer and the electron depletion layer gradually shortens, and the region between the electron depletion layer and the anode remains essentially unchanged. Therefore, the overall mobility of the material continuously increases, the effective mass continuously decreases, and the real part of the dielectric constant continuously decreases, resulting in a continuous blue shift of the device's resonant frequency.

[0037] When the dipole domains move to the vicinity of the anode, the electron depletion layer begins to be absorbed by the anode. The region between the cathode and the electron accumulation layer gradually lengthens, while the region between the electron accumulation layer and the electron depletion layer gradually shortens. As a result, the material mobility continuously increases, the effective mass continuously decreases, and the real part of the dielectric constant continuously decreases, leading to a continuous blue shift in the resonant frequency of the device.

[0038] As the dipole domains continue to move, the electron accumulation layer also begins to be absorbed by the anode. The electric field outside the domains gradually increases as the domains are absorbed by the anode. Therefore, the mobility in the region from the cathode to the electron accumulation layer continuously decreases, and thus the real part of the dielectric constant of the semiconductor gradually increases, and the resonant frequency continuously redshifts.

[0039] Therefore, in the dipole domain transit time mode, the moving dipole domains cause the high bias lateral voltage to modulate the resonant frequency of the metamaterial device in a time-varying manner.

[0040] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. An actively electrically controlled terahertz device based on a metamaterial structure, characterized in that, The device consists of a metamaterial layer structural unit (1), a substrate layer (2), a first electrode (3), a first highly doped semiconductor layer (4), a second electrode (5), a second highly doped semiconductor layer (6), and a metal plate (7). A metamaterial layer (1) is provided on the top of the substrate layer (2), and a first highly doped semiconductor layer (4) and a second highly doped semiconductor layer (6) are provided on the two symmetrical sides of the substrate layer (2). A first electrode (3) is provided on the first highly doped semiconductor layer (4), and a second electrode (5) is provided on the second highly doped semiconductor layer (6). The metamaterial layer (1), the first electrode (3), and the second electrode (5) are on the same plane. A metal plate (7) is provided below the substrate layer (2). The structural unit (1) is arranged periodically on the substrate layer (2), and the first electrode (3) and the second electrode (5) are located on both sides of the structural unit (1); The substrate layer (2) is a semiconductor material with negative differential resistance effect; The metal plate (7) is fabricated on the lower surface of the semiconductor substrate; the thickness of the metal plate is greater than the skin depth through which electromagnetic waves propagate, so as to ensure that the transmittance of the device is 0. The first electrode (3) and the second electrode (5) form ohmic contacts with the corresponding first highly doped semiconductor layer (4) and second highly doped semiconductor layer (6) below; The structural unit (1) of the metamaterial layer is one of a square, an open resonant ring, or a circular ring; The substrate (2), the first highly doped semiconductor layer (4), and the second highly doped semiconductor layer (6) are made of gallium arsenide, gallium nitride, or indium phosphide. A high bias voltage is applied to the substrate (2) through the first electrode (3) and the second electrode (5). At this time, the first electrode (3) and the second electrode (5) form a Gunn diode with the substrate, generating a negative differential resistance effect in the substrate (2). Due to the electron transfer mechanism, the carrier concentration, mobility, and effective mass distribution in the substrate will change, thereby changing the resonant characteristics of the device.

2. The actively electrically controlled terahertz device based on metamaterial structure according to claim 1, characterized in that, The structural unit (1), the first electrode (3), the second electrode (5), and the metal plate (7) are made of one of the following materials: gold, silver, copper, and aluminum.

3. The actively electrically controlled terahertz device based on metamaterial structure according to claim 1, characterized in that, The operating mode of the Gunn diode is one of the following: ideal mode, dipole domain transit time mode, electron accumulation domain mode, confined space charge accumulation mode, or quenched dipole layer mode.

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