A graphene conductance transition-based terahertz source and a working method and a preparation method thereof

Abstract

The application discloses a terahertz source based on graphene conductance transition and a working method and a preparation method thereof. The terahertz source comprises a substrate, a graphene channel layer, a source electrode, a drain electrode, a gate dielectric layer, a first gate electrode, a second gate electrode, a third gate electrode and a passivation layer. The substrate, the graphene channel layer and the gate dielectric layer are sequentially arranged from bottom to top. The first gate electrode, the second gate electrode and the third gate electrode are distributed on the upper surface of the gate dielectric layer. The third gate electrode is located between the first gate electrode and the second gate electrode and is completely covered by the passivation layer. The source electrode and the drain electrode are respectively located on the two sides of the gate dielectric layer. The graphene channel layer forms a pn junction under the regulation of the first gate electrode and the second gate electrode. Part of the graphene channel layer is reversibly transformed between a semiconductor and a semimetal under the regulation of the third gate electrode. The application effectively improves the radiation power of the graphene terahertz source.

Description

Technical Field

[0001] This invention relates to the field of terahertz technology, specifically to a terahertz source based on graphene conductivity transition and its working method and preparation method. Background Technology

[0002] Terahertz waves lie between the microwave and infrared bands in the electromagnetic spectrum, with frequencies ranging from 0.1 to 10 THz and wavelengths from 3 to 0.03 mm. Terahertz photons have low energy, causing minimal damage to biological materials and can penetrate materials such as ceramics, cardboard, and plastics. They already have important applications in non-destructive testing, biomedical diagnostics, and security monitoring. Furthermore, terahertz wave frequencies are significantly higher than the current main frequency bands for 5G communication in China (3.5–4.9 GHz), offering richer bandwidth resources and Tbit / s data transmission rates, making them promising for applications in high-speed wireless communication, inter-satellite communication, and radar communication.

[0003] Graphene, a novel two-dimensional nanomaterial, possesses excellent electrical, mechanical, thermal, and terahertz properties. While the electromagnetic properties of traditional metallic materials significantly attenuate in the terahertz band, graphene, with its Dirac cone-shaped band structure, zero effective electron mass, and a drift velocity as high as 10⁶ m / s, maintains a high response in the terahertz range. The Fermi level of graphene can be tunable through chemical or electrical doping, altering the carrier type and concentration and exhibiting p-type or n-type electron transport characteristics. By manipulating the Fermi level, pn junctions can be constructed in graphene, enabling carrier recombination and terahertz wave radiation. Compared to optically pumped terahertz sources and vacuum electronic terahertz sources, graphene terahertz sources offer advantages such as low power consumption, simple structure, and high integration. However, the on / off ratio of conventional field-effect modulated graphene is generally less than 10, making it difficult to turn off. This results in unclear pn junction interfaces, low carrier recombination, and low terahertz wave output power, which currently cannot meet the application requirements of terahertz communication. Therefore, increasing the output power can significantly improve the overall performance of graphene terahertz sources and promote the development of terahertz communication.

[0004] The invention disclosed in CN116454156A is a graphene terahertz detector integrated with a grid-like antenna and its fabrication method. By constructing a terahertz detector using a grid antenna and graphene, the carrier distribution within the channel can be adjusted at the microscopic atomic level. Furthermore, the unique grid antenna enables efficient focusing of the terahertz light field, ultimately achieving highly sensitive terahertz detection at room temperature. However, this invention cannot solve the problem of low output power of the terahertz source.

[0005] The invention disclosed in CN112379537B is a perovskite-based spatial terahertz modulator and its fabrication method. It employs a double-layer modulation structure with a bottom electron modulation layer and a top hole modulation layer, fully utilizing the accumulation effect of electrons and holes in the modulation layer to increase the utilization efficiency of photogenerated carriers, thus achieving better modulation depth for terahertz waves. However, this invention also fails to solve the problem of low output power of the terahertz source. Summary of the Invention

[0006] The purpose of this invention is to provide a terahertz source based on the conductivity transition of graphene, along with its operating and fabrication methods. This invention addresses the problem of low output power in current graphene terahertz sources, achieving a low-power, highly integrated, and high-output-power terahertz source. The device structure of this invention is simple, the process is stable and controllable, facilitating miniaturization and integration, and improving the radiation power of the graphene terahertz source.

[0007] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention discloses a terahertz source based on graphene conductivity transition, the terahertz source comprising a substrate, a graphene channel layer, a source electrode, a drain electrode, a gate dielectric layer, a first gate electrode, a second gate electrode, a third gate electrode, and a passivation layer.

[0009] The substrate, graphene channel layer, and gate dielectric layer are arranged sequentially from bottom to top; the first gate electrode, the second gate electrode, and the third gate electrode are distributed on the upper surface of the gate dielectric layer, and the third gate electrode is located between the first gate electrode and the second gate electrode and is completely covered by the passivation layer; the source electrode and the drain electrode are located on both sides of the gate dielectric layer and completely cover the edge portion of the graphene channel layer extending to the outside of the gate dielectric layer.

[0010] The graphene channel layer forms a pn junction under the control of the first and second gate electrodes, and a portion of the graphene channel layer undergoes a reversible transition between semiconductor and half-metal under the control of the third gate electrode.

[0011] Furthermore, the lengths of the first and second gate electrodes in the source-drain connection direction range from 10 μm to 100 μm, and the length of the third gate electrode in the source-drain connection direction ranges from 50 nm to 200 nm; the gap widths between the first and third gate electrodes and between the second and third gate electrodes both range from 3 μm to 60 μm.

[0012] Furthermore, the gate dielectric layer is solid and has mobile positive ions, which undergo a reversible bond-breaking process with the graphene channel layer under the drive of an electric field.

[0013] Furthermore, the thickness of the gate dielectric layer ranges from 5 nm to 30 nm.

[0014] Secondly, this invention discloses a method for operating a terahertz source based on graphene conductivity transition, the method comprising the following steps:

[0015] By applying positive or negative voltages to the first and second gate electrodes respectively, the type of charge carriers in the graphene below the gate electrodes is controlled to be n-type or p-type, thus constructing a pn junction in the graphene.

[0016] When a positive voltage is applied to the third gate electrode to the corresponding threshold, the graphene below the gate electrode undergoes a transition from a half-metal to a semiconductor, which reduces the conductivity of the graphene while increasing the carrier concentration near the pn junction, thus increasing the intensity of the terahertz wave. When a negative voltage is applied to the third gate electrode to the corresponding threshold, the graphene below the gate electrode undergoes a transition from a semiconductor to a half-metal, and its conductivity is restored.

[0017] Thirdly, this invention discloses a method for preparing a terahertz source based on graphene conductivity transition, the preparation method comprising the following steps:

[0018] S1, Graphene Transfer: A wet transfer method is used to transfer CVD graphene material covered with an Au film onto the target substrate.

[0019] S2, Graphene channel patterning: The graphene channel area pattern is prepared by photolithography and development technology, and Au and graphene outside the channel are removed sequentially by wet etching and oxygen plasma cleaning.

[0020] S3, Source / drain metal electrode fabrication: Source / drain metal electrode patterns are prepared using photolithography and development technology, and then metal layers are deposited using physical vapor deposition technology. The metal outside the electrode patterns is removed using a wet stripping process to complete the source / drain metal electrode fabrication.

[0021] S4, Dielectric growth: Using the source and drain metal electrodes prepared in step S3 as masks, Au in the graphene channel region is removed by wet etching process, and a gate dielectric layer is deposited in the entire area by thin film growth process.

[0022] S5, Gate metal electrode fabrication: The gate metal electrode pattern is prepared using photolithography and development technology, the metal layer is deposited using physical vapor deposition technology, and the metal outside the electrode pattern is removed using a wet stripping process to complete the preparation of the gate metal electrode, which is used for subsequent voltage regulation to form graphene pn junction and graphene low conductivity region.

[0023] S6, Passivation layer preparation: A passivation layer is deposited on the device surface using a thin film growth process. The excess passivation layer outside the channel region is removed using photolithography and dry etching techniques to complete the preparation of the terahertz source device.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] First, the terahertz source based on graphene conductivity conversion of the present invention, its working method and preparation method, by regulating the conductivity of graphene, increases the concentration of two types of charge carriers at the graphene pn junction interface, enhances the charge carrier recombination efficiency, and improves the terahertz radiation power.

[0026] Second, the terahertz source based on graphene conductivity transition of the present invention, its working method and preparation method, have smaller spatial variation of graphene Fermi level in the p(n) type region near the pn junction interface, which improves the monochromaticity of terahertz waves generated by carrier recombination. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the terahertz source structure based on graphene conductivity transition of the present invention;

[0028] Figure 2 This is a schematic diagram illustrating the conversion of graphene conductivity by gate voltage.

[0029] Figure 3 This is a schematic diagram illustrating the principle of enhanced carrier recombination through conductivity conversion in graphene. Detailed Implementation

[0030] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0031] See Figure 1 This invention discloses a terahertz source based on graphene conductivity transition. The terahertz source includes a substrate, a graphene channel layer, a source electrode, a drain electrode, a gate dielectric layer, a first gate electrode G1, a second gate electrode G2, a third gate electrode G3, and a passivation layer.

[0032] The substrate, graphene channel layer, and gate dielectric layer are arranged sequentially from bottom to top; the first gate electrode G1, the second gate electrode G2, and the third gate electrode G3 are distributed on the upper surface of the gate dielectric layer, and the third gate electrode G3 is located between the first gate electrode G1 and the second gate electrode G2 and is completely covered by the passivation layer; the source electrode and the drain electrode are located on both sides of the gate dielectric layer and completely cover the edge portion of the graphene channel layer extending to the outside of the gate dielectric layer.

[0033] The graphene channel layer forms a pn junction under the regulation of the first and second gate electrodes, and a portion of the graphene channel layer undergoes a reversible transition between semiconductor and half-metal through the regulation of the third gate electrode.

[0034] The terahertz source of the present invention is an all-solid-state structure. The graphene channel layer can form a pn junction under the control of the first gate electrode G1 and the second gate electrode G2. Furthermore, a portion of the graphene channel layer can undergo a reversible transition between the semiconductor and the half-metal through the control of the third gate electrode G3, thereby increasing the concentration of p-type and n-type charge carriers near the pn junction interface, enhancing charge carrier recombination, and increasing the intensity of the generated terahertz wave.

[0035] The first gate electrode G1, the third gate electrode G3, and the second gate electrode G2 are arranged sequentially along the source-drain connection direction. The lengths of the first gate electrode G1 and the second gate electrode G2 in the source-drain connection direction are 10 μm to 100 μm, and the length of the third gate electrode G3 in the source-drain connection direction is 50 nm to 200 nm. The gap width between the first gate electrode G1 (or the second gate electrode G2) and the third gate electrode G3 is 3 μm to 60 μm.

[0036] The gate dielectric layer is solid and contains mobile positive ions such as oxygen vacancies, which can undergo a reversible bond-breaking process with the graphene in the channel layer under the drive of an electric field. Preferably, the thickness of the gate dielectric layer is 5–30 nm. By applying a certain value of positive / negative voltage to the first gate electrode G1 and the second gate electrode G2, the carrier type of the graphene below the gate electrode can be controlled to be n / p type, thereby constructing a pn junction in the graphene. When a positive voltage is applied to the third gate electrode G3 to a certain threshold, the graphene below the gate electrode can undergo a transition from half-metal to semiconductor, which reduces the conductivity of the graphene while increasing the carrier concentration near the pn junction, thereby enhancing carrier recombination and increasing the intensity of terahertz wave generation. When a negative voltage is applied to the third gate electrode G3 to a certain threshold, the graphene below the gate electrode can undergo a transition from semiconductor to half-metal, and the conductivity is restored. In this embodiment, the third gate electrode G3 controls the conductivity transition of graphene in a non-volatile manner. After the gate voltage is removed, the conductivity state of graphene and the carrier distribution in the pn junction region can remain unchanged for a certain period of time. Figure 3 This is a schematic diagram illustrating the principle of enhanced carrier recombination through conductivity conversion in graphene.

[0037] The specific fabrication steps of the terahertz source based on graphene conductivity transition in this embodiment of the invention are as follows:

[0038] (1) Graphene transfer: Graphene material grown by CVD on Cu substrate is selected. A 50nm thick Au film is deposited on the graphene surface by electron beam evaporation. After the Cu substrate is removed by wet etching, the graphene + Au film is transferred to the Si / SiO2 substrate by wet transfer process.

[0039] (2) Graphene channel patterning: The graphene channel area pattern is prepared by photolithography and development technology, and only the graphene channel area is covered with photoresist. Then, the photoresist is used as a protective layer, and Au outside the channel is removed by wet etching. Then, the graphene outside the channel is removed by oxygen plasma cleaning. Finally, organic solvents such as acetone are used to remove the photoresist above the channel.

[0040] (3) Source and drain metal electrode fabrication: Source and drain metal electrode patterns are fabricated using photolithography and development technology, so that the source and drain patterns overlap with the two ends of the graphene channel region respectively. Metallization is completed by depositing Ti / Au / Ti through electron beam evaporation process with metal thickness of 20nm / 200nm / 10nm. Then, organic solvents such as acetone are used for stripping to complete the fabrication of source and drain electrodes.

[0041] (4) Dielectric growth: Au on the area of ​​the graphene channel not covered by the source and drain electrodes is removed by wet etching. Then, a dielectric layer with a thickness of 5nm to 30nm is deposited on the graphene surface using ALD or MBE process. The dielectric layer needs to have mobile positive ions, such as Al2O3 or HfO2.

[0042] (5) Gate metal electrode fabrication: The gate metal electrode pattern is fabricated using photolithography, including a first gate electrode G1 and a second gate electrode G2 for forming the graphene pn junction, and a third gate electrode G3 for manipulating the conductivity transition of graphene, such as... Figure 1 As shown, Ti / Au metallization was achieved by electron beam evaporation, with metal thicknesses of 20 nm / 200 nm. The metal was then stripped using organic solvents such as acetone to complete the gate electrode fabrication.

[0043] (6) Passivation layer preparation: A 200nm thick Si3N4 passivation layer is deposited on the device surface using PECVD process. The excess passivation layer outside the channel region is removed by photolithography and ICP etching technology to complete the preparation of the terahertz source device.

[0044] (7) Terahertz source operation: A certain voltage is applied to the first gate electrode G1 and the second gate electrode G2 respectively to induce the graphene below the electrodes into an n-type or p-type doped state. A certain voltage is applied to the third gate electrode G3 to induce a conductivity transition in the graphene below the electrode, such as... Figure 2 As shown, the magnitudes of the voltages applied to the first gate electrode G1, the second gate electrode G2, and the third gate electrode G3 are related to the thickness of the gate dielectric layer. Applying a bias voltage between the source and drain drives carrier recombination at the pn junction, generating terahertz waves.

[0045] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of this application can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0046] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, produce instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0047] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0048] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment, causing a series of operational steps to be executed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that run on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0049] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0050] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A terahertz source based on graphene conductivity transition, characterized in that, The terahertz source includes a substrate, a graphene channel layer, a source electrode, a drain electrode, a gate dielectric layer, a first gate electrode, a second gate electrode, a third gate electrode, and a passivation layer; The substrate, graphene channel layer, and gate dielectric layer are arranged sequentially from bottom to top; the first gate electrode, the second gate electrode, and the third gate electrode are distributed on the upper surface of the gate dielectric layer, and the third gate electrode is located between the first gate electrode and the second gate electrode and is completely covered by the passivation layer; the source electrode and the drain electrode are located on both sides of the gate dielectric layer and completely cover the edge portion of the graphene channel layer extending to the outside of the gate dielectric layer. The graphene channel layer forms a pn junction under the control of the first and second gate electrodes, and a portion of the graphene channel layer undergoes a reversible transition between semiconductor and half-metal under the control of the third gate electrode.

2. The terahertz source based on graphene conductivity transition according to claim 1, characterized in that, The lengths of the first and second gate electrodes in the source-drain connection direction range from 10 μm to 100 μm, and the length of the third gate electrode in the source-drain connection direction ranges from 50 nm to 200 nm; the gap widths between the first and third gate electrodes and between the second and third gate electrodes both range from 3 μm to 60 μm.

3. The terahertz source based on graphene conductivity transition according to claim 1, characterized in that, The gate dielectric layer is solid and has mobile positive ions, which undergo a reversible bond-breaking process with the graphene channel layer under the drive of an electric field.

4. The terahertz source based on graphene conductivity transition according to claim 1, characterized in that, The thickness of the gate dielectric layer ranges from 5 nm to 30 nm.

5. A method for operating a terahertz source based on any one of claims 1-4, characterized in that, The working method includes the following steps: By applying positive or negative voltages to the first and second gate electrodes respectively, the type of charge carriers in the graphene below the gate electrodes is controlled to be n-type or p-type, thus constructing a pn junction in the graphene. When a positive voltage is applied to the third gate electrode to the corresponding threshold, the graphene below the gate electrode undergoes a transition from a half-metal to a semiconductor, which reduces the conductivity of the graphene while increasing the carrier concentration near the pn junction, thus increasing the intensity of the terahertz wave. When a negative voltage is applied to the third gate electrode to the corresponding threshold, the graphene below the gate electrode undergoes a transition from a semiconductor to a half-metal, and its conductivity is restored.

6. A method for preparing a terahertz source based on any one of claims 1-4, characterized in that, The preparation method includes the following steps: S1, Graphene Transfer: A wet transfer method is used to transfer CVD graphene material covered with an Au film onto the target substrate. S2, Graphene channel patterning: The graphene channel area pattern is prepared by photolithography and development technology, and Au and graphene outside the channel are removed sequentially by wet etching and oxygen plasma cleaning. S3, Source / drain metal electrode fabrication: Source / drain metal electrode patterns are prepared using photolithography and development technology, and then metal layers are deposited using physical vapor deposition technology. The metal outside the electrode patterns is removed using a wet stripping process to complete the source / drain metal electrode fabrication. S4, Dielectric growth: Using the source and drain metal electrodes prepared in step S3 as masks, Au in the graphene channel region is removed by wet etching process, and a gate dielectric layer is deposited in the entire area by thin film growth process. S5, Gate metal electrode fabrication: The gate metal electrode pattern is prepared using photolithography and development technology, the metal layer is deposited using physical vapor deposition technology, and the metal outside the electrode pattern is removed using a wet stripping process to complete the preparation of the gate metal electrode, which is used for subsequent voltage regulation to form graphene pn junction and graphene low conductivity region. S6, Passivation layer preparation: A passivation layer is deposited on the device surface using a thin film growth process. The excess passivation layer outside the channel region is removed using photolithography and dry etching techniques to complete the preparation of the terahertz source device.

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