An ultrafast huygens super surface based on high electron mobility

Abstract

This invention discloses an ultrafast Huygens metasurface based on high electron mobility, relating to the field of terahertz device technology, and solves the problems of low modulation rate, small on / off ratio and bandwidth, and insufficient stability of existing terahertz modulators. The invention includes a semiconductor substrate, an epitaxial layer disposed on the semiconductor substrate, and a double-layer modulation unit array disposed on the epitaxial layer. Each modulation unit structure of the double-layer modulation unit array includes a cascaded I-type structure (I-2DEG) with a top layer embedded with a 2DEG and a double-slit resonant ring (DSRR) at the bottom layer. The I-2DEG includes a source resonator, a drain resonator, a gate connection line, and a semiconductor-doped heterostructure. The DSRR structure includes two split resonant rings. This invention employs a design combining a double-layer metal structure and a single-layer controllable semiconductor, achieving efficient and high-transmission terahertz wave modulation compared to other terahertz amplitude modulators.

Description

Technical Field

[0001] This invention belongs to the field of terahertz device technology, specifically relating to an ultrafast Huygens metasurface based on high electron mobility. Background Technology

[0002] Terahertz waves are electromagnetic waves ranging from 0.1 THz to 10 THz. Compared to other frequency bands, they possess unique electromagnetic characteristics, exhibiting advantages such as high frequency, wide bandwidth, strong transmission capability, and rich information carrying capacity. Metasurfaces can achieve phase modulation, amplitude modulation, beam scanning, and focusing lenses, becoming an effective technology for terahertz wave modulation. Typically, metasurface-based devices perform these functions in a flat manner with feature sizes smaller than or much smaller than the wavelength, exhibiting higher efficiency, all of which are beneficial for device integration. In recent years, more and more metasurfaces have been combined with controllable semiconductors to achieve dynamic modulation of terahertz waves through external excitation conditions. Domestic and international scholars have conducted extensive research on terahertz wave modulation, currently mainly employing temperature control, optical control, and electrical control methods. The controllable semiconductor materials used are mainly superconducting materials, doped semiconductors, vanadium oxide, and high electron mobility transistors (HEMTs), thereby achieving amplitude, phase, and frequency modulation of terahertz waves.

[0003] HEMT (Heterojunction Field-Effect Transistor) is a transistor that operates using a highly mobile two-dimensional electron gas (2DEG) in the channel, enabling it to operate at ultra-high frequencies and ultra-high speeds. HEMT works by applying an external voltage to change the height of the Schottky barrier under the gate. Due to the Schottky barrier and the movement of electrons to the undoped GaN layer, the AlGaN layer beneath the gate is completely depleted. The electrons that migrate to the undoped GaN layer form 2DEGs in the triangular wells at the heterojunction surface. These 2DEGs are spatially separated from the impurity centers in the AlGaN layer, unaffected by ionized impurities, resulting in very high mobility. Compared to other devices, HEMTs offer advantages such as low power consumption, low noise, and ultra-high speed. Furthermore, they exhibit excellent performance in terms of frequency, gain, and efficiency.

[0004] Compared to ordinary metasurfaces that utilize a single resonance to dynamically control terahertz waves, Huygens metasurfaces possess both electrical and magnetic resonance modes. By adjusting the coupling strength between these modes, electromagnetic waves can be manipulated more flexibly. In the microwave band, researchers often place controllable semiconductors simultaneously within a bilayer structure to control the surface current and create Huygens resonance. However, dynamic modulation of bilayer structures is difficult to achieve in real-time synchronization in practical applications, leading to deterioration in modulation performance. As the frequency increases and the wavelength further decreases, it becomes difficult to design bilayer dynamic structures on subwavelength substrates. Active Huygens metasurfaces in both the terahertz and optical bands utilize all-dielectric materials, which facilitates the control of Huygens resonance. However, because all-dielectric materials require the control of the entire dielectric, the device's response rate is affected. Designing a deep, high-speed, and wide-bandwidth metasurface at terahertz frequencies remains a challenge. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention proposes to provide an ultrafast Huygens metasurface based on high electron mobility, which solves the problems of low modulation rate, small on / off ratio and bandwidth, and insufficient stability of existing terahertz modulators.

[0006] An ultrafast Huygens metasurface based on high electron mobility includes a semiconductor substrate, an epitaxial layer disposed on the semiconductor substrate, and a dual-layer modulation unit array disposed on the epitaxial layer. Each modulation unit structure of the dual-layer modulation unit array includes a cascaded I-type structure (I-2DEG structure) with 2DEG embedded in the top layer and a dual-slot resonant ring (DSRR structure) in the bottom layer. The I-2DEG includes a source resonator, a drain resonator, a gate connection line, and a semiconductor-doped heterostructure. The DSRR structure includes two slot resonant rings.

[0007] Preferably, the modulation unit array includes an M*N type array composed of modulation unit structures, where M represents the number of rows of the modulation array and N represents the number of modulation units in each row, wherein M≥3 and N≥3.

[0008] Preferably, the I-2DEG structure is a vertically cascaded open I-shaped structure with four embedded high electron mobility transistors;

[0009] Preferably, the source resonator and the drain resonator are "I"-shaped structures of the same size, symmetrically arranged on both sides of the gate connection line, and are mirror images of each other. The two metal stubs closer to the gate connection line are shorter than the two metal stubs farther from the gate connection line. The short metal stubs at the ends of the source resonator and the drain resonator are connected to the semiconductor doped heterostructure through metal electrodes.

[0010] Preferably, the source resonator, drain resonator, and gate connection line form an open "I" shaped structure. The top metal structure is set as four vertically arranged open "I" shaped structures. The gate connection line is placed above the semiconductor doped heterostructure, that is, in the middle of the four slots of the I-2DEG structure, and adjacent gate connection lines are interconnected with each other.

[0011] Preferably, the gate connection line is narrower in the portion of the doped heterostructure than in other portions, making processing easier.

[0012] Preferably, each row of modulation unit structures in the modulation unit array shares the same gate connection line, and the gate connection line of each row is connected to the same negative electrode; the source resonator and drain resonator of each row of modulation unit structures are connected to the positive electrode through metal feed lines.

[0013] Preferably, the DSRR structure is placed directly below the I-shaped structure with openings at both ends of the I-2DEG structure, and the opening resonant ring has an opening angle of 60° and the opening direction is horizontal to the left.

[0014] Preferably, the metal electrode material is Ti, Al, Ni or Au.

[0015] Preferably, the semiconductor substrate is made of sapphire, high-resistivity silicon, or silicon carbide.

[0016] Preferably, the material of the doped heterojunction structure is AlGaN / GaN, InGaN / GaN, AlGaAs / GaAs, AlGaAs / InGaAs, or AlGaAs / InGaAs / InP, where the slash indicates the combination of two materials.

[0017] Preferably, the source resonator, drain resonator, gate connection line, and metal feed line are made of Au, Ag, Cu, or Al. A modulation method based on an ultrafast Huygens metasurface with high electron mobility includes the following steps:

[0018] In the metasurface, the negative voltage-loaded electrode connected to the gate connection line is loaded with a negative voltage, and the positive voltage-loaded electrode connected to the source and drain is loaded with a positive voltage. When the gate voltage is 0V, the concentration of the two-dimensional electron gas in the heterojunction remains at a high level. The source and drain resonators in the resonant unit are connected as one unit through I-2DEG. At this time, the surface current directions of the I-2DEG structure and the DSRR structure are the same. According to Ampere's law, the equivalent magnetic fields formed by the I-2DEG structure and the DSRR are opposite in direction inside the substrate, so they are equivalently canceled out, forming only independent electric resonances.

[0019] When the applied voltage is aV, the I-shaped structure at both ends of the DSRR and I-2DEG structures and the surface current of the DSRR structure are opposite, which induces an equivalent magnetic current. The I-shaped structure in the middle of the I-2DEG structure still exhibits electric resonance. Therefore, as the applied excitation changes, the resonance mode of this structure changes from a single electric resonance to an electromagnetic hybrid mode. When the two resonance modes exist at the same time, perfect transmittance is produced, which is the Huygens resonance mode.

[0020] The value of 'a' ranges from -6V to 10V.

[0021] The beneficial effects of this invention include:

[0022] 1. This invention provides an ultrafast Huygens metasurface, which is designed using a combination of a double-layer metal structure and a single-layer controllable semiconductor. This design breaks through the limitation of the response rate of previous all-dielectric structures for modulation. By adopting the Huygens (electromagnetic resonance hybrid mode) design scheme, it can achieve efficient and high-transmittance modulation of terahertz waves compared with other terahertz amplitude modulators. Experiments show that the transmittance of terahertz propagation at 321 GHz increases from 0.273 to 0.911, and the modulation efficiency is 90.5%.

[0023] 2. This invention provides an ultrafast Huygens metasurface, which is designed with a double-layer metal structure. When terahertz waves pass through the double-layer metal structure, the different resonant frequencies of the metal structure cause resonance superposition, thereby expanding the bandwidth. In actual tests, the bandwidth with a modulation efficiency greater than 50% is 176 GHz.

[0024] 3. This invention provides an ultrafast Huygens metasurface, which uses a high electron mobility transistor as its modulation device. The high mobility of the two-dimensional electron gas in HEMT allows the metasurface to switch rapidly between different resonant modes. Therefore, the modulator has a very high modulation rate, and an ultrafast Huygens switching of 167 ps was achieved experimentally.

[0025] 4. The modulation unit array formed by metamaterial design in this invention is a two-dimensional planar structure that can be realized through microfabrication. The process is mature and easy to manufacture, avoiding the high processing difficulty brought about by complex three-dimensional structure design schemes.

[0026] 5. The present invention designs a transmissive terahertz wave modulator, which is simpler to operate and more convenient to use than a reflective modulator, and is especially effective in terahertz point-to-point communication. Attached Figure Description

[0027] Figure 1 This is a top view of the overall structure of the device in the embodiment.

[0028] Figure 2This is a three-dimensional schematic diagram of the Huygens metasurface unit structure in the embodiment.

[0029] Figure 3 The diagram shows the front and back sides of the Huygens metasurface unit structure in the embodiment.

[0030] Figure 4 In the example, the Huygens metasurface was used at a carrier concentration of 1e14 cm⁻¹ -2 The surface current and magnetic field strength distribution at 333 GHz.

[0031] Figure 5 In the example, the Huygens metasurface was used at a carrier concentration of 2e10cm⁻¹. -2 The surface current and magnetic field strength distribution at 333 GHz.

[0032] Figure 6 The figure shows the S21 parameter diagram of the Huygens metasurface simulation in the example.

[0033] Figure 7 The image shows the terahertz wave waveform transmitted through the Huygens metasurface when an externally applied 6 GHz modulated voltage signal is applied.

[0034] Figure Labels

[0035] 1-Positive voltage applied electrode, 2-Negative voltage applied electrode, 3-Modulation unit array structure, 4-Modulation unit structure, 5-Semiconductor substrate, 6-Epipolar layer, 7-Source resonator, 8-Drain resonator, 9-Gate connection line, 10-Ohmic contact electrode, 11-Semiconductor doped heterostructure, 12-I-2DEG structure, 13-DSRR structure. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0037] Example 1

[0038] The following is in conjunction with the appendix Figure 1-7 Specific embodiments of the present invention will be described in detail;

[0039] An ultrafast Huygens metasurface based on high electron mobility, in this embodiment, includes a semiconductor substrate 5, a modulation unit array structure 3, a positive voltage-loaded electrode 1, and a negative voltage-loaded electrode 2; as shown... Figure 1 As shown, the modulation unit array structure 3 includes multiple modulation unit structures 4 arranged in an array, and the modulation unit structures are connected in series in the form of parallel circuits.

[0040] like Figure 2 , Figure 3 As shown, the modulation unit structure 4 includes an I-2DEG structure 12 and a DSRR structure 13. The positive voltage loading electrode 1, the negative voltage loading electrode 2, the I-2DEG structure 12, and the DSRR structure 13 constitute a metal structure layer, and an epitaxial layer 6 and a semiconductor substrate 5 are sequentially disposed below the metal structure layer. The resonant structure in the I-2DEG structure 12 includes four sets of vertically cascaded source resonators 7 and drain resonators 8.

[0041] The source resonator 7 and drain resonator 8 are the same size and form an "I"-shaped metal structure. The lower horizontal metal stubs of the "I"-shaped metal structure are shorter than the upper horizontal metal stubs. The source resonator 7 and drain resonator 8 are placed as mirror images of each other with gate connection line 9, forming an open "I"-shaped structure. The long horizontal stubs of the "I"-shaped structure are interconnected and connected to the positive voltage loading electrode 1. The I-2DEG structure 12 contains four high electron mobility transistors, which are respectively embedded in the slots of the open "I"-shaped structure, i.e., between the short side stubs of the source resonator 7 and drain resonator 8. Each high electron mobility transistor is composed of a source, drain, gate line, and a semiconductor-doped heterostructure 11.

[0042] All the source resonators 7 and drain resonators 8 of the modulation unit structure are connected to the same electrode for feeding, and the gate connection line is connected to the same electrode for feeding.

[0043] The DSRR structure 13 includes two open-ended resonant rings, which are respectively placed directly below the open-ended I-shaped structures at both ends of the I-2DEG structure. The open-ended resonant rings have an opening angle of 60°, and the opening direction of both rings is horizontally to the left.

[0044] In this embodiment, the semiconductor substrate 5 is made of SiC, the epitaxial layer 6 is AlGaN / GaN, the ohmic contact electrode 10 is made of Ti, and the I-2DEG structure 12 and DSRR structure 13 are made of Au.

[0045] The physical mechanism of the HEMT-based Huygens metasurface is to utilize the 2DEG carrier concentration in the HEMT to regulate the electronic transport state in the top I-2DEG structure 12, thereby changing the relative phase of the currents in the two-layer structure, realizing an ultrafast transformation from electrical resonance to Huygens resonance, and thus regulating the transmission of terahertz waves.

[0046] The specific modulation method is as follows: a negative voltage is applied to the negative voltage loading electrode 2 connected to the gate connection line 9 in the metasurface, and a positive voltage loading electrode 1 connected to the source and drain is applied to the positive voltage loading electrode 1. For example... Figure 4 As shown, when the applied voltage is 0V, the concentration of the two-dimensional electron gas in the heterojunction remains at a high level. The source resonator 7 and drain resonator 8 in the resonant unit are connected as one unit through I-2DEG. At this time, the surface current directions of the I-2DEG structure 12 and the DSRR structure 13 are the same. According to Ampere's law, the equivalent magnetic fields formed by the I-2DEG structure 12 and the DSRR are opposite in direction inside the substrate, so they are effectively canceled out, forming only independent electric resonances. Figure 5 As shown, when the applied voltage is -7V, the I-shaped structures at both ends of the DSRR and I-2DEG structures 12 and the surface current of the DSRR structure 13 reverse, resulting in an equivalent magnetic current. The I-shaped structure in the middle of the I-2DEG structure 12 still exhibits electric resonance. Therefore, as the applied excitation changes, the resonance mode of this structure changes from a single electric resonance to an electromagnetic hybrid mode. When the two resonance modes exist simultaneously, perfect transmittance is generated, which is the Huygens resonance mode.

[0047] like Figure 6 As shown in the simulation, the terahertz propagation transmittance changes from 0.294 to 0.925 at 333 GHz, the modulation efficiency is 90.3% at 333 GHz, and the bandwidth with a modulation efficiency greater than 50% is 187 GHz.

[0048] like Figure 7 As shown in the figure, after experimental testing, the modulator has a fairly high modulation rate, and the experiment achieved an ultrafast switching of Huygens 167ps.

[0049] This invention utilizes microfabrication technology to effectively combine HEMT and a dual-layer modulation unit array. By applying an external voltage excitation to control the carrier concentration of the two-dimensional electron gas in the top layer, it alters the relative phase of the currents in the top and bottom layers, achieving an ultrafast transition from electrical resonance to Huygens resonance and controlling the propagation of terahertz waves. Simulation calculations demonstrate that this Huygens metasurface achieves a modulation efficiency of 90.3%, with a bandwidth of 187 GHz exceeding 50% modulation efficiency. In actual dynamic testing, an ultrafast switching of 167 ps for Huygens was achieved, exhibiting high modulation efficiency and a large modulation depth. Experiments also demonstrated its extremely high modulation rate.

[0050] In summary, the ultrafast Huygens metasurface based on high electron mobility transistors is a terahertz wave control device with great development potential and practicality. It not only breaks through the limitation of the traditional dynamic Huygens metasurface's two-layer control, but also overcomes the problem of slow response rate of all-dielectric dynamic Huygens metasurfaces. More importantly, it provides a new approach for low-loss, high-efficiency, and high-speed terahertz dynamic control, and also provides new ideas for the development of beam control and digital high-speed dynamic control metasurfaces.

[0051] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A high electron mobility based ultrafast Huygens super-surface, characterized in that, It includes a semiconductor substrate (5), an epitaxial layer (6), and a modulation unit array with a double-layer structure designed sequentially from bottom to top; the modulation unit array with a double-layer structure includes multiple modulation unit structures (4), the modulation unit structure (4) includes a top layer of nested 2DEG cascaded I-type structure, i.e., I-2DEG structure (12), and a bottom layer of double-opening resonant ring, i.e., DSRR structure (13). The I-2DEG structure (12) includes: a source resonator (7), a drain resonator (8), a gate connection line (9), and a semiconductor doped heterostructure (11); the DSRR structure (13) includes two open resonant rings. The source resonator (7) and drain resonator (8) are both "I" type structures of the same size. They are symmetrically arranged on both sides of the gate connection line (9), and the two metal stubs closer to the gate connection line (9) are shorter than the two metal stubs farther away from the gate connection line (9). The short metal stubs at the ends of the source resonator (7) and drain resonator (8) are connected to the semiconductor doped heterostructure (11) through metal electrodes. The I-2DEG structure (12) includes multiple open "I"-shaped structures composed of source resonators (7), drain resonators (8), and gate connection lines (9). The metal part at the top of the I-2DEG structure (12) is set as multiple vertically arranged open "I"-shaped structures. The gate connection lines (9) are placed above the semiconductor doped heterostructure (11), that is, in the middle of each slot of the I-2DEG structure (12). Adjacent gate connection lines (9) are connected to each other. The DSRR structure (13) is placed directly below the I-shaped structure with openings at both ends of the I-2DEG structure (12).

2. The ultrafast Huygens metasurface based on high electron mobility as described in claim 1, characterized in that, The modulation unit array includes an M*N type array composed of modulation unit structures (4), where M represents the number of rows of the modulation array and N represents the number of modulation units in each row, where M≥3 and N≥3.

3. The ultrafast Huygens metasurface based on high electron mobility as described in claim 1, characterized in that, The gate connection line (9) is narrower in the portion of the semiconductor doped heterostructure (11) than in the other portions.

4. The ultrafast Huygens metasurface based on high electron mobility as described in claim 1, characterized in that, Each row of modulation unit structure (4) in the modulation unit array shares the same gate connection line (9), and the gate connection line (9) of each row is connected to the same negative voltage loading electrode (2); the source resonator (7) and drain resonator (8) of each row of modulation unit structure (4) are connected through a metal feed line and connected to the positive voltage loading electrode (1).

5. The ultrafast Huygens metasurface based on high electron mobility as described in claim 1, characterized in that, The metal electrode material in the I-2DEG structure (12) is Ti, Al, Ni or Au.

6. The ultrafast Huygens metasurface based on high electron mobility as described in claim 1, characterized in that, The doped heterojunction structure in the I-2DEG structure (12) is made of AlGaN / GaN, InGaN / GaN, AlGaAs / GaAs, AlGaAs / InGaAs or AlGaAs / InGaAs / InP, where the slash indicates the combination of two materials.

7. A modulation method based on an ultrafast Huygens metasurface with high electron mobility according to any one of claims 1-6, characterized in that, Includes the following steps: In the metasurface, the negative voltage loading electrode connected to the gate connection line is loaded with a negative voltage, and the positive voltage loading electrode connected to the source and drain is loaded with a positive voltage. When the gate voltage is 0V, the concentration of two-dimensional electron gas in the heterojunction remains at a high level. The source resonator and drain resonator in the resonant unit are connected as one unit through the I-2DEG structure. At this time, the surface current directions of the I-2DEG structure and the DSRR structure are the same. According to Ampere's law, the equivalent magnetic field formed by the I-2DEG structure and the SRR is opposite in direction inside the substrate. Therefore, they are equivalently canceled out and only independent electric resonances are formed. When the applied voltage is aV, the I-shaped structure at both ends of the DSRR and I-2DEG structures and the surface current of the DSRR structure are opposite, which induces an equivalent magnetic current. The I-shaped structure in the middle of the I-2DEG structure still exhibits electric resonance. Therefore, as the applied excitation changes, the resonance mode of this structure changes from a single electric resonance to an electromagnetic hybrid mode. When the two resonance modes exist at the same time, perfect transmittance is produced, which is the Huygens resonance mode. The value range of 'a' is -6V to -10V.

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